Abduction Is Love: Several Ashikabi are known to forcefully wing Sekirei against their will. Mitsuha describes the process as "taming" them, suggesting once winged, a Sekirei will develop feelings whether the bond was consensual or not.
Accidental Marriage: You may say this when Minato winged Tsukiumi and Kazehana as both of them said they are his wives. Musubi and Kusano also claim to be his wife, though Musubi didn't seem to know what this actually means.
Accidental Pervert: Minato, though usually the result of the action of one or more of his haremettes.
Achilles' Heel: All winged Sekirei have one, in the form of their Sekirei Crest. If exposed, an opponent need only touch it and recite their Norito for an One-Hit Kill.
He also appears to have genuinely cared about Takehito and has thus far honored his request to not involve Miya in the Sekirei Plan.
The Ageless: Sekirei appear to not age in the same manner as humans. It is shown that the five eldest Sekirei (#01 - #05) are fully grown adults while many of the others are still infants. A brief flashback shows Miya saying her farewells to an infant Tsukiumi, before she retired from the Discipline Squad. Likewise, Karasuba and Yume were fully grown adults when Musubi met them as a small child.
Almost Kiss: Played with during the 3rd Match. Natsuo repeatedly asks his Sekirei if they want to use their Norito, causing them to get flustered and excited. Benitsubasa makes a huge deal about it and bickers with Haihane over who gets to go first. She wins the argument, but just as she leans in to get her kiss....Natsuo's phone rings.
Animal Motif: Musubi with Bears is an obvious one, but a more subtle one is Tsukiumi; a number of her attacks are named after and carry the appearance of snakes or serpents or her hair went wiggling like a snake everytime she is angry.
The Sekirei as a whole have a motif involving birds. This makes sense since the Sekirei is a type of bird, also known as the Wagtail. Shinto creation myths credit these birds with teaching the gods Izanagi and Izanami to love.
Anti-Magic: Seo can surpress a Sekirei's ability as long as he's touching them. Or, more accurately, groping them.
Anti-Villain: Uzume - taking out Sekirei like a hitman and not even following the customs of honoring one's opponent, but only because she's being blackmailed with her Ashikabi's life on the line.
Mikogami is beginning to slide into this as well, along with his two primary Sekirei (Akitsu and Mutsu).
Art Evolution: To be expected, after 140 chapters and counting....
As You Know: Minato accidentally invokes this on Matsu in season two when she mentions there were now rumours about a Sekirei and Ashikabi escaping the plan.
Minato: But they're not rumours! They really did escape!
Matsu: I know. I was there.
Author Appeal: Ahika Sakura seems to really like busty girls and bishounen.
Babies Ever After: The original Sekirei and their Ashikabi that survived went on to have children. This is where the modern Ashikabi come from.
Bad Powers, Good People: Shiina, Yukari's Sekirei, has powers that make everything rot and die but he is one of the kindest and sweetest people in the manga and is actually scared by Yukari's brutal treatement of defeated Ashikabi.
Badass: Every Sekirei is supposed to be this to varying extents.
Badass Biker: Matsu, in the anime. Sanada of the West is also one.
Badass Bookworm: Again, Matsu. She is one of the single-digit Sekirei, after all. If she has to fight, she will turn into a biker babe with a bazooka.
Badass Crew: Minato, Seo, and Sanada's harems all count.
Badass Normal: Seo and Sanada, who both ignore the rule about Ashikabi not fighting. Minato by the end of Season 2. He fought Haihane to save Kazehana, and was doing a damned good job considering Haihane could've sliced him to ribbons had it not been for being dizzy from the fumes of alcohol, and he also survives several things like having a roof collapse on him, and takes so many wounds for his Sekirei he's practically Made of Iron. And, by the end of Season 2, having the sheer balls to stand up to Karasuba, especially when she could have effortlessly killed him, should be proof positive he's taken several levels in badass.
He actually managed to knock out Haihane in the Sake warehouse twice.
Little Miss Badass: Kusano, at least at anime episode 11 where she carried a big grenade launcher atop Matsu's motorcycle.
Just to illustrate how badass Miya is, during the invasion of the island in the Back Story the other 4 disciplinary members went around taking out tanks and helicopters. While Miya, cut battle cruisers in half lengthwise, from a cliff without breaking a sweat.
Bad Ass Decay: Haihane and Benitsubasa. In Season 1, they were pretty tough, but in Season 2, while Beni beats one random Sekirei up, they both aren't nearly as tough as they were earlier. Even Minato manages to land a couple of hits on Beni, and rolls a bottle on a slightly tipsy Haihane, who trips on it.
Bash Brothers: Common among teams with multiple Sekirei. Musubi with Tsukiumi, Homura with Kazehana or Tsukiumi. Sanada's trio as well.
Battle Harem: Minato is the primary example, but Sanada's Power Trio and Seo's twins count as well. The villainous examples play with this, in completely different ways: Mikogami has a collection rather than a romantic harem, Higa considers his harem to be employees, and the Discipline Squad suffer from Incompatible Orientation with their Ashikabi.
Bears Are Bad News: Musubi occasionally has an animal avatar of a bear appear behind her, and the bear fist is one of her attacks.
Bee People: The Sekirei are hinted to be this, as Takami once explained to Kusano that #01 was "their queen". Miya is vague about exactly what she is, but clarifies that she is something completely different from her "107 feathers".
Beauty Is Never Tarnished: While they do get visibly injured in battle, Haihane is the only Sekirei thus far to have any visible scarring. It's suggested that they heal better than humans, and MBI provides them with exceptional medical treatment when necessary. Karasuba mentions that she only has a small scar left after Miya nearly killed her, thanks to MBI's treatment.
It's not clear whether the ghostly head is something she invokes or if it's a visual shorthand for the respectful terror other Sekirei have for her.
She also can do it over the phone, which freaks the hell out of Seo. Minato uses this against him when he initially wants to charge Haruka for helping escape the city with Kuno. Although Seo agrees to it, he puts Minato in a headlock afterwards. Nevertheless, he sticks to his word and helps out as much as he can.
Shiina, who more than earns his title as "Death God".
Minato himself, once he begins to fight seriously with the intention of winning the Sekirei Plan. He proves to be an excellent strategist and takes full advantage of his harem's strengths and unique abilities.
Bi the Way: Minato, Yukari, Musubi, Homura, and Mutsu. Several other characters are more ambiguous but may be this as well, such as Uzume and Mikogami.
Big Ball of Violence: Seo and the Ashikabi of the West get into one because of mist, complete with fighting sounds. In season 1 Seo gets his ass kicked by his own Sekirei for being a pervert in this manner.
Big Bad Wannabe: Nothing definite, but certain chapters seem to have Higa headed in this direction. His team was pretty much Curb Stomped during the third fight of the third round, and Minaka seems to be becoming interested in taking him out.
Big Brother Instinct: Minato, Shiina. Kazehana also states many of the Single Numbers feel this way towards the rest of the Sekirei, which makes it a Tear Jerker since they're pretty much guaranteed to end up terminating their little sisters (and brothers).
Big Damn Heroes: Tsukiumi does this at the end of Season 1, but it's subverted because she's fighting 2 against 1 and as a distraction, so she ultimately loses. Played straight with Yume when she emerges shortly afterwards.
Big Eater: Every single Sekirei out there, but especially Musubi who finishes a meal for ten by herself in episode one.
Big Good: Minato, by virtue of having the majority of the good guy Sekirei at his command. Seo is a lesser example, and Miya is a psuedo mix of this and Harem Nanny.
Biker Babe: In a surprising bit of anime-original material, Matsu, and it makes her come off as a genuine Badass Biker instead of a lame attempt at Fanservice as well.
Bishounen: The extremely rare male Sekirei are this, if Mutsu, Shiina, Amebane, and Homura are any evidence.
Blessed with Suck: If you think about it, most Ashikabi's have this. They have been given a hot member of the opposite sex who loves them completely, and perfectly understands them. Then they have to watch them fight to the death (or whatever it is) with other people, or you lose him/her. And to top it all off, you know the other people your fighting are fighting for the exact same reasons and just lost the person they love because of you.
Book Dumb: Minato is actually very intelligent, but he does badly in school since he cannot perform well when under pressure.
Bound and Gagged: Happens to Musubi in the Sekirei Diagnosis OVA - when Karasuba offers to measure her, she ties Musubi up in the measuring tape. Musubi complains about the tape being too tight, but the noises and expressions she makes indicate she's loving every moment of it.
Born Winner: The Single Numbers, who are inherently more powerful than other Sekirei. Mutsu hints that this is because their further development when found meant that MBI had less of a chance to control their powers.
Bridal Carry: Minato does this for Musubi in the first episode when she's unable to move in an attempt to escape from Hikari and Hibiki.
Minato whenever his Sekirei are fighting over him.
Matsu to Homura, and especially Miya anytime she accidentally does/says something Miya doesn't like.
Minaka to Takumi. While he may be the CEO of MBI, that doesn't stop her from whacking him if she feels he's stepped out of line.
Everyone beaten up by Yukari while she's helping Shiina search for Kusano.
Benitsubasa towards Haihane, and in one episode, to Kusano and Kazehana, who both hang up the phone on her when she's trying to blackmail Musubi. The look on her face is hilarious after they hang up on her.
Cast Herd: Primarily divided along the territories of the major Ashibaki — North (Minato and his allies), South (Mikogami's group), East (Higa's group), and West (Sanada's trio), as well as the employees of MBI.
Cat Fight: Completely avoided. While there is Clothing Damage and plenty of other bits of fanservice involved, the fights are treated seriously and can be downright brutal.
Cat Smile: Musubi and Kuu tend to display one when they're happy.
The Champion: Uzume to Chiho, Mutsu and Akitsu to Mikogami, Shiina to Yukari and Kusano.
Changed My Mind, Kid: Tsukiumi comes to help out at the end of episode 12 after Miya gives her a pep talk about how the other girls are in the lead against her because she was refusing to help while the other three girls did what they could. Subverted in that she doesn't stop the two discipline squad members, although she did delay them.
Played straight with Uzume as well. She decides to help Kuno escape rather than kill her as ordered to.
Cheaters Never Prosper: Higa engages in a variety of schemes to defeat MBI and Minato, including blackmailing Uzume and Shiina into working for him, kidnapping Yukari with the intention of forcing her to marry him, and stealing the Jinki from others. This eventually leads Mikogami to step in, as well as triggering his Villainous Breakdown after Minato's team rescues Chiho, terminates four of his Sekirei, Uzume betrays him, and Yukari sets fire to his penthouse before escaping with Shiina. Even though he's one of the last Ashikabi standing, he's completely outmatched by the others and has essentially lost all his former edge.
Chekhov's Gunman: All the Sekirei that Minato come to wing appear in the 3rd chapter (or 0.3), except Kuu, and even she got a mention. Akitsu also appears...
Kaho and Oosumi are first spotted when Homura recalls his time serving as the Sekirei Guardian. They later show up, and turn out to be a fairly significant pair.
In a one-shot omake and Drama CD, an Ashikabi and Sekirei get blasted off into the distance by Shiina after they were fooled into accepting a fake bounty on Yukari. They later show up at the beginning of the 4th Match, just in time to create a panic by recognizing Yukari and Shiina. We later learn they managed to escape the city, and ended up befriending Haruka and Kuno. Their news about the current events in the Sekirei Plan inspire Haruka to write Minato a letter encouraging him to win.
Clark Kenting: Spoofed. Kagari is absolutely baffled at Tsukiumi's inability to recognize him as Homura just because of the black mouth-cover he wears when fighting. When Tsukiumi finally connects the dots◊, she quite visibly feels like a moron.
Also seen in the anime when Tsukiumi saves Kagari, who's not wearing the mask at the time. JustifiedIn-Universe with remarks by Homura mentioning later that she didn't see his face because it was really dark in the alley at the time, and later in Season 2 when Tsukiumi also mentions that she didn't take a good look at his face because it wouldn't be proper.
Musubi also once thought Homura was Kagari, and then did a doubletake and said it wasn't him because Kagari "doesn't wear a mask".
Cliff Hanger: Season 1 ends with Haruka and Kuno successfully escaping, but a lot of loose ends are shown which have yet to be resolved, and Minaka mentions that the game is far from over, which ultimately leads into the second season.
Clingy Jealous Girl: Tsukiumi changes from a Tsundere to this after her winging, Kusano also appears to learn to behave this way from her. Also Hikari and Hibiki (the former having a shorter fuse than the latter) do not let Seo to wing another Sekirei, and will immediately zap him if they catch him trying to do that. They don't mind if he takes a male one like Shiina though.
Although its very subtle, when Musubi sees Minato getting a little too friendly with Tsukiumi, a bear aura will pop up behind her briefly, which scares them the same way Miya's aura does.
Closet Key: A bisexual-variant. Minato and Homura are this to each other, and Mikogami is implied to be this for Mutsu.
Clothing Damage: Musubi is especially prone to this; her clothing must be made of tissue paper. Justified in how Sekirei are beating the crap out of each other with various supernatural abilities, most of which are more than strong enough to destroy easily clothing and buildings but leaving Sekirei fairly intact, and Musubi in particular has to get close to punch them... Apparently strongly enough to strip them, too.
Used as a common tactic in duels, since the Sekirei Crest at the base of their neck provides a One-Hit Kill.
Color-Coded Characters: All of the Sekirei have different hair colors, and wear different clothing to make it easier to tell them apart. Slightly subverted at first with Kagari, Takami, and Takehito, as they have similar hair color/styles.
Color Failure: Matsu completely whites out when Minato innocently asks who Sekirei #01 is, right before Miya shows up.
A random guy loses his color after Yukari kicks him in the groin to try and get info from him on Kusano's whereabouts.
In episode 8, after hearing Matsu mention a Sekirei mysteriously defeating and leaving their opponents before MBI can confirm the fight, Minato has a talk with all his current Sekirei about it, since he's worried about their safety. Both Tsukiumi and Musubi mention that they want to fight her since she's so strong, and develop a Battle Aura. Even Kuu develops one, much to Minato's chagrin. Matsu meanwhile, continues to snicker at his inability to control the situation.
Later in Season 2, after Matsu reveals she was one of the original 5 Sekirei, Minato and some of the others are surprised at this fact. She reveals some more information, but they're still completely shocked at the fact that she was one of the original Discipline Squad members. She puts on a cute pouty face afterwards.
Mutsu makes a heartfelt confession of his devotion to his master, using video game comparisons. Mikogami takes this to mean if he wins, he'll get all the Sekirei and be the only one playing~! Mutsu wonders if he was even paying attention at all.
Compressed Adaptation: A fine example, too. The anime uses only the most important bits, moving along at a brisk pace.
Covert Pervert: Yukari at first appears to be a very well off, but soon, you see her getting Nose Bleed around Shiina and even struggling trying not to peek at him taking shower. She later tries to grope Tsukiumi in Season 2, but the latter runs off before she gets a chance to. The face she makes creeps out Tsukiumi in the process.
Cross-Popping Veins: Several characters display one from time to time, especially Tsukiumi when the other Sekirei try to claim them over her.
Curb-Stomp Battle: In the manga and anime, we're shown an invading international army against the first disciplinary squad. Army lost big time, and there were only 5 of them(sekirei). Later this is proven even more when Karasuba massacres so many soldiers their bodies pile on each other.
Musubi loses somewhat easily to Benitsubasa, but then when Yume takes control of Musubi's body temporarily, she easily defeats both Benitsubasa and Haihane.
Karasuba and Shiina are both infamous among the Sekirei for these.
Dark and Troubled Past: The first generation Discipline Squad: Miya, Matsu, Kazehana, Karasuba, and Mutsu, who were forced to slaughter human armies to protect the 103 infant Sekirei. For Karasuba, it may have been her Start of Darkness, since she enjoyed killing so much. The others eventually walked away from it, and avoid talking about it. It's safe to assume the person responsible for erasing all data on the 1st generation was Matsu.
Akitsu due to the events that caused her to become a Scrapped Number. The Tuner that messed her adjustments up was fired as a result, and took out his rage on Akitsu. He told her everything was her fault, and attempted to strangle her to death for being a failure.....forcing her to kill him in self-defense.
Minaka often welcomes players trying to change the rules a little bit, and will act accordingly to counteract their plans, such as sending troops to the area Minato is trying to help Haruka and Kuno escape. Even at the end of Season 2, Matsu mentions hacking Minaka's spacecraft to leave him hopelessly stranded in orbit, but she says that he'll probably figure out how to regain control (which he does a few moments later, and makes a point to mention that).
The Discipline Squad knows exactly where to go when Minato is trying his escape plan at the end of Season 1. And in Season 2, after their first fight, Benitsubasa closes off the walls to force Kazehana to fight in a small area where she can't use her wind magic effectively. Haihane does something similar with Tsukiumi, luring her into a room where she can't easily escape with her water magic.
Miya and some other residents of Maison Izumo seems to know a lot more about the Sekirei plan and MBI's ambitions than they should. However, its gradually revealed that they knew about Minaka's plans all along, and either tried to fight against it, or else ran away to avoid taking part in it. Miya claims she could kill Minaka if asked to, but Matsu mentions that the city would get destroyed in the process.
Sort of. In the anime, she is confirmed (by an onscreen computer screen) to be still alive, but greatly injured. In the manga, it has been said that if Minato wins the tournament, he can bring Uzume back.
Declaration of Protection: One of Minato's motivation for helping out the Sekirei. This is also why Haruka took pity on Kuno and decided to be her Ashikabi.
Musubi "And I even protected my modesty this time."
Arrows point out that she's only wearing panties.
Demon Head: Done mostly by Miya It seemed she learned from her husband, Asama Takehito, back when she first was being adjusted
Somehow, Yukari later learn to do it as well, and thus the title 'Demon Ashikabi'.
Denied Food as Punishment: Miya often threatens to do this to Seo, and Matsu when she's fooling around with Minato, and by extension, Minato.
Depraved Bisexual: Yomi. People also think the Ashikabi of the North (Minato) is this, due to the rumors about his harem.
Deserted Island: Kamikura Island, a mysterious island that rose up out of the sea and revealed the crashed Sekirei ship. Minaka initially hoped that it would turn out to be a Monster Island as well. He got Human Aliens instead.
Disappeared Dad: The only mention of Minato's father is 'unknown', by Matsu. You just know something's up when the information Sekirei has no clue.
Or more likely, Miya's forbidden her to reveal it.
Pretty much confirmed to be Minaka.
Distressed Damsel: Yukari becomes this for awhile. It is eventually subverted when she realizes she shouldn't just be waiting for a rescue and starts trying to escape on her own. With a Slasher Smile to boot!
When Karasuba rants to Musubi about how glorious their final battle will be, she grabs her roughly, shoves her against the wall and the hilt of her sword presses up against Musubi like an erection, all while wearing a crazed, lustful expression. It's one of a handful of instances in the series of one character coming on to another that isn't played for laughs.
Sekirei can be winged against their will, by any Ashikabi that is able to kiss them. It is described at one point as "taming" them, and Mikogami's attempts to capture first Kusano, and later Shiina, have a rather disturbing undertone to them.
Double In-Law Marriage: Technically, since Sekirei consider the bond with their Ashikabi to be equivalent to marriage. Minato and Yukari's respective Sekirei, Kusano and Shiina, consider each other to be siblings.
Tsukiumi towards Minato (usually in the form of using water on him).
Yukari towards various male Ashikabis (although in one case, the guy deserved it for pulling a knife on her after he lost his Sekirei battle to her).
Made all the more striking by the introduction of an abusive Male Sekirei and his female Ashibaki. On the surface, his actions aren't much different (mocking, yelling at, pushing around) but it is played as deadly serious and a Moral Event Horizon.
Double Take: In episode 8 of the first season, Minato feels at ease after having a private talk with Tsukiumi about her not losing a fight, which he had with Musubi in an earlier episode. He then wonders out loud if they're not the same despite their differences. He opens the door slightly, and sees Musubi standing by the door. He nonchalantly closes it for a few moments, then opens it again, and after she says something to him, he screams, wondering if Musubi just heard what he said comparing the two girls.
The Dragon: Each villain seems to have one. Minaka has Karasuba, Mikogami has Mutsu, and Higa has Kakizaki. Taken from the viewpoint of other Ashikabi, Shiina is this to Yukari.
Dragons Up the Yin Yang: The Sekirei crest includes a taijitu (the Yin Yang symbol). Tsukiumi and Homura also each use a dragon-themed attack.
Due to the Dead: One of the rules of the Sekirei Plan requires the victor to stand guard over their terminated enemy until MBI is able to retrieve the body. Musubi in particular in shown to take this very seriously, watching over them with a somber expression. That Uzume does not do this is considered a serious offense, earning her the label of a "heretic".
Cranked Up to Eleven in the Pure Engagement OVA Two Gossips Topic, which chronologically takes place after Season 1 but before Season 2, features a Measuring Day in the first half, and a Beach Episode in the 2nd half. Virtually all of the main women in the show are topless for pretty much the entire episode.
Fate Worse Than Death: Broken bonds are considered this by the Sekirei, who would rather tolerate a cruel Ashikabi than lose their bond. Akitsu's situation as a Scrapped Number also counts, as she is incapable of being winged in the first place.
Full-Contact Magic: Many Sekirei's abilities function like this, channeling their powers through weapons or physical attacks.
Furo Scene: The Izumo inn's bath provides many opportunities.
Also, there was an omake story specifically about a trip to a "neutral ground" hot spring.
Gecko Ending: The anime diverges from the manga around the time Homura gets winged. In the manga, Stage 3 starts immediately after this, while Minaka only hints at starting it at the end of Season 2 of the anime. Uzume's arc gets drastically changed as well. Minaka still offers to help in both versions, but in the manga Uzume was still alive when they got her to MBI, and she saves Minato rather than Musubi in the manga, and Minato doesn't play as active a role in the manga of helping Chiho. Nor did Minaka implement the rule of deactivating Sekirei with no wins, or blow his building up (yet anyway...) in the manga.
Kazehana also gets "winged" right after Minato helps Kuno and Haruka escape in the manga, whereas in the anime she does it in Season 2. She also takes a much more active role in helping out in the manga, rather than the subtle offscreen help she provides in the anime.
Glowing Eyes of Doom: Miya will use these if she is really pissed off. Hikari and Hibiki also use this when they are angry with Seo. Yukari starts sporting it later as well.
Groin Attack: Yukari's favorite way to 'punish' abusive Ashikabis. This is because Shiina refuses to do it for her.
Guy on Guy Is Hot: Matsu gets a ...suspicious... look when Seo wants to "get along with" Minato as men during the hot springs omake. She's also very interested in asking her old squadmate about his male Ashikabi.
Matsu:Mutsu-tan! Mutsu-tan! Matsu has always wanted to ask! Why did you choose a male Ashikabi to....hehehe!
Half-Human Hybrid: All modern Ashikabi are the descendants of matings between Sekirei and humans several centuries ago, and still close enough to their non-human heritage that that the jinki classify them with Sekirei rather than humans.
This is further driven home when they arrive on Kamikura Island, and learn that the island gives off unique energy due to centuries of exposure to the Sekirei's ship. Humans are immune to it, and Sekirei filter it harmlessly through their cores.....but the energy is toxic to Ashikabi since their bodies absorb it like a Sekirei, but lack a core to process it safely.
Hammerspace: Matsu pulls a large gun on Musubi in the bath, even though she's only wearing a towel. Minato even lampshades this.
Harem Nanny: Miya, though she comes down hard on anything too ero-ero in the house.
Heel-Face Turn: Hikari and Hibiki, who started out attacking Musubi and were longtime enemies of Homura. They quickly become some of Minato's most important allies, once he moves into Izumo Inn and becomes friends with Seo.
At the end of a battle between Minato and Higa's Sekirei, Toyotama attempts to kill Musubi by stabbing her with a lance before fleeing. Musubi is saved, however, when Uzume jumps in her way and gets herself stabbed instead. Uzume would die from her injuries shortly afterwards.
In the manga, Uzume tried to block the attack from Higa's Sekirei which was aimed at Minato.
Takehito focused the unstable power of the Jinki on himself to save Minaka, Takami, and the Sekirei unable to flee the MBI building.
Heroic Second Wind: Musubi or is it Yume? recovers at the end of episode 12 to beat up the Disciplinary Squad after Minato's Heroic Resolve to not abandon his friends and Sekirei helps to revive her.
Hollywood Tactics: An invading army with tanks, helicopters and ships? Group the Tanks within spitting distance of each other. The same for the helicopters that are maybe 50 ft in the air directly above the tanks. And have your support warship hanging out right off the coast.
Hope Bringer: Higa pretends to be one on occasion, in order to manipulate other Ashikabi. Being the real deal, Minato is not fooled.
Hostile Show Takeover: The On the Next for Pure Engagement episode 0 is an extended skit with the entire cast declaring what the new season will be about. Needless to say, their ideas on it vary considerably.
I Didn't Mean to Turn You On: The Sekirei realizing who their Ashikabi are get horny when wanting to get winged. And poor Minato, even AFTER winging his Sekirei, most of them still get horny and want/find ways to get laid by him, they HORRIBLY fail thanks to Miya.
Idiot Hair: Musubi, Hikari, Shijime, Kujika, Mikogami, and Karasuba.
The 4th Stage centers on this trope, as two teams of Sekirei are forced to fight in a sealed area. If one team hasn't terminated the other within an hour, both teams will be terminated — Sekirei and Ashikabi alike. The first match-up? Minato vs. Seo, forcing the longtime allies to fight to the death.
It Amused Me: Minaka's Sekirei Plan game. While he has a set of rules regarding the Sekirei plan, he will often set up a new rule or change his plans slightly based on what's going on. Such as killing off any Sekirei with no wins within a certain period of time to encourage them to fight, setting up obstacles to prevent some Ashikabi/Sekirei from escaping the city, or agreeing to help Minato, but then making a bunch of other Ashikabi attack him before he can get to MBI's headquarters. Will generally earn him a Mega Ton Punch from Takami once she gets wind of changes to his plans.
Jerk Ass: Pretty much everyone else outside of Izumo Inn, including Minato's mother and sister. The more sympathetic ones are typically portrayed as Jerks With A Heart Of Gold.
Outright aversions include #95 Kuno (Haruka's Sekirei), #107 Shiina (Yukari's Sekirei) and Chiho Hidaka.
Ashikabi of the East, Izumi Higa, takes the cake however. Hell, even Minaka doesn't give a crap about him anymore and wants him out of the Sekirei Plan.
Seo Kaoru, at least his two Sekirei will 'discipline' him if he goes too far. Hikari and Hibiki somewhat count as well, given they were introduced targeting unwinged Sekirei for practice yet are good-natured deep down.
Seemingly that Ashikabi of the West guy too, since he's almost a carbon copy of the above (something lampshaded in the actual manga)
Haruka Shigi as well. He can be blunt, thoughtless and short-tempered, but cares enough about Kuno that he despite her plain appearance, she's his Sekirei and nobody else. He even refuses to force her participation in a 'Game' they can't win.
Kill Sat: Matsu has full control of one. Probably one of the reasons why she holds so much influence in the Sekirei game.
Kung-Fu Wizard / Magic Knight: Sekirei with Abilities or Elemental powers are almost always skilled fighters in their own right, combining their powers with physical attacks to devastating effect.
Let's You and Him Fight: Minaka sends an email to all the Ashikabi that a "certain group" of people were going to storm the MBI buildings. He set a new rule that anyone who stops that group from reaching the building would be exempt from his earlier rule where an Ashikabi with no wins would lose their Sekirei. Naturally this causes a lot of other people to try and stop Minato, and it appears he has no way out. Fortunately for him, a biker guy arrives late to the situation, and immediately trash talks some of them, then picks a fight with all of them.
Tsukiumi sometimes does this with Minato's other Sekireis.
Like Brother and Sister: Shiina and Kusano. It's suggested other sequential Numbers may consider each other siblings, as well.
Limit Break/Super Mode: All winged Sekirei have a special ability, the Norito, which can only be activated by kissing their Ashikabi and reciting their unique incantation.
Limited Wardrobe: Justified, as each Sekirei has an assigned outfit and most don't bother with civilian clothing. MBI sends deliveries of replacement clothing whenever they suffer Clothing Damage in battle.
Unlimited Wardrobe: Uzume tends to wear the same two iconic outfits, but is shown to have a near limitless collection of outfits in her closet. She lends them out to the other Izumo Inn residents.
Musubi when it comes to Minato. She has a bear avatar, for crying out loud!
Miya. The things it is hinted she will do if anyone actually asked for her help will send a shiver down your spine.
Man in White: Minaka Hiroto, Mikogami Hayato, and Higa Izumi. It's worth noting that out of the six male antagonists of the series, the half that wear something other than white are The Dragon to one of the above men in white.
Manipulative Bastard: Higa, and how! Blackmailing Uzume, kidnapping Yukari and messing with Shiina's head (leading him to almost rape Yukari), using Uzume and Shiina to cheat at the game, cheating at the game in general, trying to join forces with Minato (which is either very stupid, what with holding his sister captive and all, or full-on Magnificent Bastard territory).
Musubi really likes to do this to Minato as well in the anime.
The Masquerade: Sekirei are a carefully-guarded company secret, and Ashikabi are warned to never reveal their involvement in the Plan. Since MBI controls most of the capital, they're able to manipulate the media and come up with cover stories to explain the strange goings-on of the Sekirei Plan to the public.
Mutual Masquerade: Minato is forced to keep Musubi's true nature a secret from everyone, and has to come up with varying excuses as his harem grows. Then.....it turns out everyone living at Izumo Inn already knew about the Sekirei Plan. Keeping the secret prevents Yukari from finding out #108 has been safely with her brother the whole time.
Measuring Day: The Sekirei Examination Day omake, rife with competition over bust sizes and Les Yay.
Mission Control: Matsu acts as this most of the time, providing Minato with intel from her computer room.
Mistreatment-Induced Betrayal: Uzume was tasked with defeating Kuno, but at the end of episode 12, helps them with their plan to escape the city, along with Kazehana.
Mon: Sekirei are essentially a humanoid version, along with (usually) being a Magical Girlfriend to their Ashikabi.
Mook Horror Show: Both seasons of the anime begin with one, from the point of the view of human soldiers facing Sekirei. The second season is notable in particular, as it shows the Invasion of Kamikura Island from the point of view of the military.....then several episodes later, we see the same incident from the other side. It's a powerful reminder of how dangerous the Sekirei truly are.
Most Writers Are Male: Averted; the Mangaka is a woman, but the female characters are incredibly busty either way.
Mukokuseki: The Ashikabi characters manage to avoid this for the most point, with similar facial features, black or brown hair, and dark eyes. The Sekirei seem to follow the trope, but they're aliens.
Muscles Are Meaningless: Musubi and Benitsubasa are prime examples, though very few Sekirei look as strong as they actually are. Buff Sekirei do exist, but only one of them is a Power Type and another is a Red Shirt brutally taken down by Benitsubasa.
Time to Unlock More True Potential: A combination of Miya's training, and a hefty dose of The Power of Love. She notes that a Sekirei's true potential is further unlocked through the strength of their bond with their Ashikabi and the state of their emotions. Training can only do so much, if their bond isn't strong enough. When Homura is winged, Musubi and Tsukiumi both manifest new abilities in response.
Sekirei #00/01 Miya is so feared that no one will normally dare venture in the northern section of the city where she lives. Considering what kind of power she showed in a flashback at the beginning of Season 2, you can't blame them. This is also the reason why Seo devises the escape plan in the northern part of the city at the end of Season 1, as there will be less MBI-affiliated Sekirei/Ashikabi there.
The demon Ashikabi title, which was given to Yukari due to her tendency to viciously assault any Ashikabi she ran into in order to ask where Sekirei No. 108 is. This hilariously gets some Ashikabi's to run away during one fight in Stage 3 in the manga.
The Single Numbers are the equivalent of this trope for the Sekirei, as this signifies not only that they are the eldest and therefore the most experienced.....but also that they are inherently more powerful than their younger counterparts. The first five in particular tend to inspire Oh Crap moments among other Sekirei, thanks to their status as Super Prototypes.
Nice Job Breaking It, Hero: One of Seo's girls accidentally zaps him during the escape plan at the end of Season 1. This fries the cellphone he was using to communicate with Matsu. This justifies him being unable to help out the other people or give/receive updates to what's going on with the plan, and all he can do from that point is lay low.
No Accounting for Taste: It's heavily hinted that Kazehana once was attracted to Minaka, of all people! And, if true, this would further confirm Minaka is Minato's father, as Kazehana seemed to think he was very similar in appearance to the man she first fell for.
No Biological Sex: Homura had no set gender to begin with. He asked to be adjusted to become a male, but once he began to react to Minato's presence his body took the matter in to its own hands and has switched over to female while retaining her male mind. To date, s/he's still somewhat disoriented as to her body's reactions, and there's a Running Gag where s/he can't decide whether to go in the male or female side of baths or changing rooms.
Hermaphrodite: Homura's feminine body structure and breasts remain, but it is heavily implied that he retains a certain significant male part. At least, it would seem so when the entire harem is shown nude — Homura and Minato are the only ones with their groins covered.
Nose Bleed: Minato, obviously. Surprisingly, Yukari is also prone to this, being a Bishōnen fangirl.
Oblivious Younger Sibling: An intresting subversion. It's against the rules to talk to Muggles about the Sekirei plan, so Minato isn't allowed to talk to his sister about it. She, however knows and is in fact a part of the Sekirei plan, but for the same reasons doesn't talk to her brother about it. Unfortunately her main reason for becoming a part of the game is to look for Kuu, her Sekirei's little sister and her brother's Sekirei, leading to a case of Poor Communication Kills.
Inverted later on. While Minato is still in the dark about it, Yukari has known the identity of their father for quite some time.
Oh Crap: The look on the Disciplinary Squad when Yume shows up. More so on Haihane than Beni.
They invoke it by name earlier when Tsukume identifies herself as #09.
Olympus Mons: The ancient Sekirei from the other seven ships, beings so incredibly powerful that Minato's Sekirei are in awe of their strength. They may or may not have inspired some of the ancient myths, and their Ashikabi were noted to have amassed incredible authority over their homelands and fought epic wars with each other.
The One Guy: Male Sekirei are this, by default, since males are exceptionally rare. In particular, Mutsu for both the 1st generation Discipline Squad and the South. Homura becomes this for the North, leading Mutsu to express his sympathy over having to deal with "those witches".
Only Mostly Dead: Uzume and the other terminated Sekirei who suffered wounds that should be fatal. It is suggested that the winner will be able to reactivate them, though Miya states that a broken bond is the equivalent of death to a Sekirei and that the Uzume they knew is gone.
Only Six Faces: Common with the Sekirei. It evens gets mentioned in-universe, as many Sekirei resemble each other.
Painting the Medium: Kazehana talks to Minato with heart-shaped speech bubbles at one point. Miya swiftly forbids them.
Panty Fighter: True to the trope, most of the Sekirei (the ones who wear panties) end up with at least one Panty Shot.
Paper-Thin Disguise: Matsu's "disguise" while hiding from MBI in season two is nothing more than a babushka. Lampshaded by Homura.
Don't tell me that's your entire disguise.
Parental Abandonment: Apart from the missing father, Minato and Yukari's mother pretty much left them to be raised by their grandmother. Turns out their mother is working for MBI, essentially as The Dragon. She seems to care more about her Sekirei "children" than her actual ones...
Mikogami's parents completely ignored him in favor of their work, when they weren't shipping him off to other countries for acting out.
Petite Pride: Kusano, she is rather proud of her lack of assets.
Poor Communication Kills: Shiina's search for Kuu wouldn't last very long if Yukari ever bothered to just go to Maison Izumo. Justified however, in that neither Yukari nor Minato knows that the other is involved in the Sekirei program, and Minaka did plainly warn Minato in the first episode (and probably every other Ashikabi as well) that if they ever reveal the Sekirei plan to a non-participant, they'd be punished severely for it. Seeing as how Minaka has eyes and ears all over the place, Minato not wanting to explain why he's suddenly living with even more women, including Tsukiume, and Kusano, and all the other crazy stuff going on around them, it's hard to blame her entirely.
Power Limiter: Matsu states that one function of the adjustments was this, limiting their natural powers to a more manageable level. Homura believes this to be one reason that Akitsu was scrapped, since her power is not as limited and controlled as other Sekirei.
The Power of Love: A major theme of the series, as all Sekirei draw strength from their bond with their Ashikabi. The deeper the feelings between the two, the stronger the Sekirei can become.
Power Tattoo: The Sekirei Crest. It appears on the base of their neck when a Sekirei is winged, and vanishes when they cease functioning. Doubles as an Achilles' Heel.
Pretty Freeloaders: Mostly avoided with Minato's harem, due to Miya requiring them to earn their keep with household chores. Mikogami's harem plays it straight, living off his family's wealth and behaving like a bunch of Rich Bitches.
The Promise: Musubi and Karasuba promised to be the final two Sekirei standing, and to face each other in the final battle.
It turns out that Minaka promised Takehito that he would not involve Miya in the Sekirei Plan, allowing her to live in peace after his Heroic Sacrifice.
Psychic Link: All Ashikabi and Sekirei share one, as part of their bond. Shiina and Kusano are also shown to have one, due to their strong telepathic abilities and bond as siblings. Ashikabi with multiple Sekirei can also act as a psychic intermediary between their partners, allowing them to combine their powers and create a Combination Attack.
Mind Link Mates: Most pairs are this, able to sense emotions and share dreams.
Real Women Don't Wear Dresses: Subverted. The majority of Sekirei are extremely feminine, and don't concern themselves with how feminine or masculine their peers are. Minato's harem are among the strongest Sekirei around, and very feminine whether they're kicking ass or cooking lunch.
Red Shirt: Most Sekirei are doomed to be this, because of the very nature of the game. Higa treats his army of Sekirei as disposable Mooks, while pretty much any Sekirei that encounters the Discipline Squad is going to be Monster Munch.
Retired Bad Ass: Miya, although in the manga it seems she may be coming out of it.
Roaring Rampage of Revenge: A variation of this occurs in episode 10 of Season 2. At Minato's request, Matsu hacks into Higa's business accounts and essentially bankrupts his business, partly to force Higa to contact Minato, and largely as payback for him being responsible for Uzume's death. The speed and zeal in which she does this scares Minato a little bit.
Running Gag: Minato's harem drawn as macho, muscular men......wearing the exact same outfits. Featured in manga omakes and the first season ending as Minato's reoccurring nightmare.
Parodied with one omake of Natsuo's nightmare, which is the Discipline Squad dressed up as cat-girl maids all speaking to him with heart-shaped speech bubbles.
Run or Die: When the Black Sekirei, Karasuba decides to fight Mitsuha and Akitsu, the latter tells the former to run or she'll die. Mitsuha ignores the warning and is quickly killed while Akitsu ran away and lived.
Sacred First Kiss: For Sekirei, being winged is at least the equivalent of this, if not their true first kiss. Yukari states that winging Shiina was her first kiss.
Sailor Earth: Out of the canonically established 108 Sekirei, only about half that number (58, currently) have been introduced or at least given names. There's still plenty of room for Fanon to make new Sekirei.
Say It with Hearts: Quite a few characters. Benitsubasa is prone to saying it with STARS, including her named attacks.
Scary Shiny Glasses: Matsu gets a chance to do this once or twice. Minaka also does this ALL the time that we rarely see his eyes through his glasses.
Screw Destiny: What Minato hopes to do. Yukari and Shiina also do this, quitting the Sekirei Plan once they confirm that Kusano is safe.
Screw the Rules, I'm Doing What's Right!: Minato does this so that the weak Kuno and her Ashikabi can flee the city. This comes back to bite him later, when he is forced to fight against the Disiplinary Squad, once in the act and again in the third round as punishment.
Secret Keeper: Miya appears to know a lot about the characters, but doesn't tell anyone until absolutely required, such as the existence of Sekirei, and about Kagari's true identity.
Seo, Hikari and Hibiki, Uzume, and all of the Single Numbers except for Tsukiumi and Akitsu are sworn to secrecy about the identity of Sekirei #01. Minaka also honors this secret, and allowed #01 to remain outside the Sekirei Plan because this was Takehito's dying wish.
Kazehana knows about Uzume's secret, but chooses not to stop her nor will she allow anyone to harm her whenever she's around.
Also forced upon all Ashikabi upon winging a Sekirei. They are not to tell anyone not involved in the Sekirei plan about it, under threat of retaliation from MBI should they leak the info.
Sensible Heroes, Skimpy Villains: It seems to be played straight in the first few chapters, with Musubi's outfit far more modest than Hikari and Hibiki's S&M gear outfits. However, it ends up being zigzagged like crazy the more Sekirei that are introduced — Sanada's Sekirei have some of the smallest outfits around, but are cheerful and kind-hearted. Meanwhile, some of the most modestly dressed Sekirei are Ax-Crazy villains.
Sensitive Guy and Manly Man: Minato and Kagari are a twist on this, in a way. Minato is definitely the sensitive one of the pair, while Kagari is a Badass and a Ladies' Man until his gender begins to change. Even so, Minato states that he considers Kagari's a "cool guy" that he deeply admires. Mikogami and Mutsu are a villanous example, as well.
Sexy Santa Dress: Several pieces of art feature Minato's Sekirei, as well as Hikari and Hibiki, in these. Parodied with Homura, who tells the audience to not be disappointed that the outfit has pants instead of a miniskirt.
Shoot The Ashikabi First: Attacking an Ashikabi is strictly prohibited by MBI, because their death will terminate all their Sekirei. Higa's Sekirei seem to make it a standard policy to target enemy Ashikabi if the battle is going poorly. Oriha, in particular, makes multiple attempts on the lives of other Ashikabi during the 3rd Match.
Shrouded in Myth: All the major Ashikabi, as well as the first generation (#01 - #05) have various myths surrounding them. The myths surrounding Minato and Seo, in particular, are hilariously off the mark.
Sitting on the Roof: Kazehana hangs out on the roof frequently, but it seems to be a common place for the residents of Izumo Inn to go.
Single Woman Seeks Good Man: A majority of the Ashikabi are sweet, normal guys. Minato, in particular, manages to win over each of his Sekirei through his kind heart.
Snow Means Love: Haruka and Kuno met on a snowy day, when he saw her shivering in the cold and took pity on her. Mikogami and Mutsu may also count.
So Proud of You: In the manga, after Minato refuses to back down from a confrontation with Takami, she states as his mother she's so proud of the man he's becoming. .......then she breaks out the Slasher Smile and sics MBI soldiers on him anyway.
Split Personality: Musubi. Sekirei No. 8, Yume, is inside of her. Yume is a love-crazy beam-user type, but while Musubi knows she has Yume's soul inside of her, she remembers nothing she's done as Yume.
Standard Female Grab Area: Minato seemingly knows how to do this properly, though it usually makes whoever he did it to call him a pervert.
That's because in the manga at least, he grabbed Yomi round the middle and copped a feel.
Played deadly straight with Seo, since when he is touching a sekirei, he effectively neutralizes their power until he lets go.
Submissive Badass: Many Sekirei are this, deferring to their Ashikabi and calling them "Master", and even tolerating mistreatment from guys they could toss around with little effort.
Super Prototype: Numbers 01 - 05 are this, having been given special adjustments that drastically increased their power. With the possible exception of Matsu, each of them is a One-Man Army and the reason other Sekirei fear the Single Numbers so much.
Sword Fight: In the penultimate episode of the 2nd season, there is a brief duel between Karasuba and Mutsu. She's bored waiting until she can confront Musubi, and figures he'll be able to keep her amused for a while. In the end, she decides she's had enough fun and wanders away, leaving Mutsu to make a hasty retreat.
Team Mom: Miya Asama, landlady of Izumo Inn. Though, she will become angry if called this; she thinks of herself as more of a Cool Big Sis
Technical Pacifist: Minato is a frail peace-loving guy who is uncomfortable with having his Sekirei or anybody else fight and wishes he could avoid conflict as much as possible. That said, it doesn't take much for something to get him to voluntarily join or even start a fight to help somebody else.
Lampshaded in Minato's first Stage Three duel, when his strategy to minimize fighting consists largely of Demolish the surrounding area and beat up everyone before the dust settles. Homura notes that for something Minato came up with to avoid conflict, it sure included a lot of wanton destruction.
Technopath: Matsu has the ability to look into any computer system with her mind and even hacks into and spys through MBI's sattelites at various points. This has caused her to be labelled "The Sneaking Sekirei" a title she doesn't appreciate.
Telepathy: All Sekirei have it, to one degree or another. Kusano is stated to have particular strong abilities, which allowed her to call out to Minato.
Tempting Fate: After Minato nods off in the bath in episode 1 of Season 2, Musubi calls him for dinner, then decides to get in the bath with him. After he wakes up, he comments that it would be bad if the other girls saw them like that. Cue Tsukiumi and Kusano opening the door to the bath...
The Only One Allowed to Defeat You: Tsukiumi uses it on Minato as a threat. Played straight with Karasuba defeating Musubi, who stops herself from fighting Yume at the end of episode 12 in Season 1 after she comments that Musubi needs to train more if Beni beat her.
"The Reason You Suck" Speech: Kuu berates Tsukiumi for not wanting to help with Minato's plan to help Kuno escape with Haruka. Miya later helps snap her out of her refusal to help.
Musubi and Minato essentially tells this to the Ashikabi and Sekirei who confront them in Season 2 and ask for his participation in escaping, after the latter Ashikabi continually insults Haruka and Kuno as being weak and pathetic.
Mikogami delivers one to Higa, when the South shows up to help defend Maison Izumo. His accurate assessment of Higa's jealousy towards Minato for overcoming the restraints of his family and society, as well as the threat of all out war between the South and East, force Higa to back down.
The Unreveal: Seriously, is there anyone (other than Minato) who doesn't know Miya is Sekirei No. 1? If you couldn't already guess it, the beginning of episode 1 in Season 2 gives it away, but it's still kept as a huge secret/surprise in-universe. In the Manga, it's not as readily apparent because of the pacing, but once Sekirei with numbers begin appearing in mass and the background info picks up, it's not a difficult concept.
This Is Unforgivable: Minato states that he won't forgive anyone that treats Sekirei like tools, or mocks the struggles of weaker, loving pairs like Haruka and Kuno.
It's Personal: Higa in particular becomes the focus of Minato's wrath, when his manipulation of Uzume is revealed and she performs a Heroic Sacrifice. From then on, he starts fighting to win and reminds people that's a good idea to Beware the Nice Ones.
Those Two Bad Guys: Benitsubasa and Haihane once they make more regular appearance, though occasionally joined by Karasuba.
Hikari and Hibiki, in their first two appearances.
Mikogami and Mutsu, occasionally joined by Akitsu as a bystander to their conversations.
Troll: Takami, Minato's mother, of all people, does this in episode 3 of Season 2. After Tsukiumi starts talking to her in the hospital, his mother tells her that she should be addressing her as "mother" (due to Tsukiumi's "marriage" to Minato), while making the same scary face Yukari does (minus the red eyes). Tsukiumi immediately apologizes and calls her that, only to have Takumi nonchalantly says she wasn't serious about it, which ticks off Tsukiumi.
Truce Zone: There are several within the capital, primarily areas owned and operated by MBI. This allows the company to perform monthly examinations on the Sekirei and keep the peace during a game of There Can Be Only One. The Northern portion of the city is considered this to a degree, as most Sekirei are too frightened of the legendary Hannya of the North to dare causing trouble in her territory. Miya strictly enforces a "no fighting" rule within Izumo Inn, which the smart people respect.
True Companions: After Karasuba defeats Musubi at the end of episode 12 in Season 2, the rest of Minato's harem move in to protect her. Karasuba taunts them that they still wouldn't be able to defeat her, but ultimately lets them go, either because she knew they saw through her bluff, or perhaps she wants Musubi to get stronger for more of a challenge.
Shown even earlier in Episode 8 of Season 1: Despite Musubi and Tsukumi constantly fighting one who Minato's "true wife" is, they agree - through "a most secret exchange" - that they trust to each have the other's back, with Tsukumi actually calling Musubi "friend."
Tsundere: Tsukiumi, Hikari. Later on, Homura towards Minato as well; albeit a bit more subtly than the first two examples. Homura punches him in the face right after getting all blushy and dere, for crying out loud.
Twenty Minutes into the Future: 2020, which really doesn't seem that different from today. Then again, take a look into the world today: There's still ten years to go yes, but is there really that much differnce?
Twinkle In The Sky: Yume did this to Benitsubasa and Haihane at the end of first season (by throwing them instead of Megaton Punch). Repeated later by Kazehana.
Tyke Bomb: The Sekirei are an entire species of tyke bombs, raised by MBI and aimed primarily at each other.
Unwanted Harem: Subverted; while at first Minato's reluctant and unwilling to take responsiblity, he eventually goes after four of his eventual six Sekirei.
We Have Reserves: Higa treats his Sekirei this way, which comes back to bite him since he does not in fact have reserves. Out of his original dozen Sekirei, he's down to his last three and things do not look good for him, since his potential opponents in the 4th Stage each have a founding member of the Discipline Squad in their ranks.
What Measure Is a Non-Human?: One of the undertones of the series. Minato treats his Sekirei as normal people, while most Ashikabi treat them as things.
Which makes it all the more painful to watch other Ashikabi who did clearly treat their Sekirei's as people as well, and then having them get defeated by another who probably didn't want to fight them in the first place if not for Minaka's constant rule changing.
When It All Began: Miya provides insight into several key events that shaped the current situation.
The great battles between the Sekirei from the other 7 ships and their Ashikabi. The survivors of these battles are the ancestors of modern Ashikabi.
The discovery of Kamikura Island by Minaka and Takami, which resulted in the formation of MBI and the awakening of the Sekirei.
The first Invasion of Kamikura Island. This final event resulted in not only the formation of the original Discipline Squad, but inspired Minaka to change the S-Plan from a research project focused on the study and protection of the Sekirei to the current Sekirei Plan.
Another significant event, of course, was the kidnapping of Musubi as a child, which resulted in Yume giving the damaged fledgling her core.
White Shirt of Death: Uzume, in the manga. Minato, also wearing a white shirt at the time, ends up completely covered in her blood.
Wholesome Crossdresser: Yukari puts Shiina in a dress to hide him from pursuers, fortunately he is so bishounen that he looks like a girl.
World of Action Girls: Sekirei are incredibly gender-skewed, with only 4 known males out of the 108. And one of those ends up as a hermaphrodite. Most Ashikabi are Non-Action Guys, and the rules of the game actually prohibit them from being involved in combat.
Would Hit a Girl: Played with in both directions. Since most of the Sekirei are female, the few males have absolutely no issue with fighting them seriously. Evil characters, such as Junichi and Amebane, are also shown to consider hitting women for annoying them to be perfectly acceptable. Both get what's coming to them courtesy of Yukari and Shiina.
Yin-Yang Bomb: Tsukiumi and Homura combine their attacks into a giant steam dragon. It's said that this can only be done with Sekirei with a shared Ashikabi, or at least a very high synchronisation.
You All Look Familiar: The male characters in particular all look relatively alike (along with spiky-haired female characters). Invoked, as quite a few Sekirei with sequential Numbers look nearly identical and have similar powers.
You Are Number Six: The Sekirei, numbering from #01 - #108. Numbers 01 - 09 are known as the "Single Numbers", and considered the most powerful.
You Gotta Have Blue Hair: Sekirei are the only ones (with the exception of MBI scientists) to have unusual hair colors. While the majority have brown or blonde hair, white is also quite common, with the occasional pink, purple, or green.
Younger Than They Look: The Sekirei were discovered 21 years prior to the series, when all but #01 were either infants or fertilized eggs. Numbers 01 - 05 have been shown to have been adults when the others were still infants, but how quickly Sekirei actually reach physical maturity is unclear. Either way, it's easy to forget that they are all younger than Minato.