The Lemon Beach House, run by the Aizawa sisters, is booming with customers in the middle of the summer. This peace will be short-lived. A girl calling herself "Ika Musume" (Squid Girl) emerges from the sea, stating her goal of taking over the world as a revenge on humanity for polluting the oceans. This army of one has a long way to go, though. When she breaks a large hole in the beach house, the sisters force Ika to work for them until she can pay for the repairs. Thus begins a cute comedy about the friends at the Lemon Beach House and world domination... supposedly.Based on Masahiro Anbe's manga, Shinryaku! Ika Musume -The invader comes from the bottom of the sea!- was adapted into a twelve episode anime in fall 2010. It's currently licensed and dubbed by Media Blasters.Season 2, titled Shinryaku!? Ika Musume, aired in fall 2011.Both seasons can be watched legally on Crunchyroll (subbed), and the first season is also on Netflix (dub).
Ika Musume contains examples of:
A-Cup Angst: When Ika Musume had 3D glasses on and wanted "to feel something that's supposed to be there, but isn't" on her friend Kiyomi. She wasn't too happy about the words, but acknowledged that she only started "growing up" in that area. This led to Kiyomi wishing that her breasts were bigger in one episode
Nagisa displays some of this when she starts crossdressing and Chizuru suggests they wrap her chest "just in case".
In the manga version of "Won't You Study?", Ika gives Eiko her "simplified" calculation method immediately after Eiko begs for it and the chapter ends shortly after. The anime adds in a scene where Ika is running Eiko ragged in the restaurant and trying to show off her math skills.
Special mention goes to the Sick Episode (Episode 8-1 and Chapter 103), which not only blended another Sick Episode, chapter 70, into the anime version, but turned the manga's ending into an entire episode, namely 8-2.
In chapter 49, "Won't you lose weight?", it's discovered that Ika actually weighs quite a bit more than she appears. Eiko forms a few theories as to how, but the actual reason remains a mystery. When this got adapted in episode 2-3 of the second season, the question was answered: Ika's bracelets are devices that allow her to freely manipulate her body weight, usually increasing it to counterbalance herself when she lifts heavy objects with her tentacles. However, she can also decrease her weight to the point that she can fly by spreading her tentacles like wings.
The "Won't You Keep It?" segment was Sanae's dream.
And in S2 E6, Mini-Ika's adventure is all Goro's dream.
All Part of the Show: during the Nohmen Rider stageshow, Chizuru is disguised as Nohmen Rider Hannya, allowing her to bust out her Crazy Awesome moves in full view of the public. Which happens again in ep. 12.
Always a Bigger Fish: invoked in ep. 11 when Ika and the family hike up a mountain, encountering animals that keep getting scared off by bigger or more dangerous animals, culminating in a king cobra. Amazingly, it doesn't bite Ika - it curbstomps her.
Apathy Killed the Cat: Eiko is the one who most actively challenges Ika, but she's more concerned about getting work done. Takeru considers her a playmate. Chizuru cares about her getting work done. The fact that she's a talking squid girl is of no importance. Nagisa is the only one that seems to care that Ika's something not seen in this world.
Arrow Catch: Sanae, of all people, nullifies an arrow trap aiming for her head in season 2's episode 6 part II. Lampshaded by the fact it was her who set the trap in the first place. But still, catching an arrow barehanded with two fingers is pretty impressive for a normal human girl.
Beam-O-War: Done in Season 2's Episode 11: Ika Musume faces off against a machine meant to replace her and the fight devolves into a ink spitting battle.
Beware the Nice Ones: Do not mess with Chizuru, her family, or her store. She will hurt you. It wasn't until the scientists turned the store invisible by accident that everyone else realized what Ika feels from Chizuru on a daily basis.
Bifauxnen: In chapter 148/Episode 2 of season 2, Eiko makes Nagisa dress up as a guy to attract more female customers.
Birthday Episode: In one episode, Squid Girl discovers the surface dwellers' custom of birthday parties, and declares today to be her birthday to take advantage of the goodies.
Bishie Sparkle: Chizuru turns up the sparkles to convince Goro to watch Takeru for her. It works.
Blatant Lies: When Ika gets amnesia in episode 7.2 in Season 2, Cindy and Sanae concoct a made up story of how she's an alien (Cindy) and fell in love with Sanae at first sight (Sanae). Ika nearly falls for it until Eiko tells them to stop trying to screw up her memory.
In chapter 110, Chizuru is definitely NOT using her pedometer for a diet... Yeah, right...
Bowdlerise: In the manga, when we first see Chizuru get serious, she cuts off Ika's tentacles with a knife. In the anime, she does it with her bare hands, though, that probably made her look more badass.
Camera Fiend: Sanae has entire photobooks of Ika, and more or less holds her hostage to get more. The so-called invader is powerless against this.
Card-Carrying Villain: Ika Musume is not a fan of the "winning the people's hearts" method of world-conquering, and considers being fearsome and terrifying to be job requirements. Nothing depresses her more than people thinking she's nice, and consequently she has a soft spot for Nagisa (who's scared to death of her).
Chekhov's Gun: Ika mourning over an empty squid hat is justified - because it's fatal.
Chekhov's Gunman: Noh Mask Rider Hannya, Chizuru's disguise, although she fake-reveals herself to be Eiko, who is introduced once in one of the earlier episodes, but makes a second appearance in the final episode of season one.
Remember Takeru's teacher, who only appeared in the anime once? She's Nagisa's older sister.
Chew Toy: Ika during the mountain episode, literally. A ridiculous amount of animals come to her because they want to eat her tentacles. Hilarity Ensues.
Sanae attempts to give up on Ika, and the results are not pretty. She starts seeing Ika everywhere she goes...
Used again when Ika tries to give up shrimp.
Combat Tentacles: Ika's... hair/tentacles/whatever are quite strong and versatile; they're able to punch through concrete, move fast enough to break the sound barrier and extend to ridiculous lengths, yet also precise enough to thread needles. Additionally, just like a normal squid, she's able to regrow them in the event that they're chopped off, albeit much faster.
Comedic Sociopathy: In universe example: When Eiko sends Ika Musume and Nagisa on a shopping trip together she states that she hopes it will help them get along better (make Nagisa see Ika Musume isn't scary) Chizuru says "I thought you sent her along because it's funny".
Comic Book Time: If this page is any indication, the entire series since Cindy's introduction has taken place during her summer vacation. That's around 200+ chapters, which either speaks poorly of the passage of time or positively of her benefits at work.
Comically Missing the Point: In the jellyfish collecting contest designed to clean the ocean of jellyfish, Clark wins by collecting one jellyfish, and creating dozens more with a duplication ray.
Companion Cube: Ika's Umbrella in Episode 8. She doesn't give it up, however, in the Couch Gag.
Cosmetic Catastrophe: A tiny bit of makeup flatters Ika very nicely, but then she tries to figure out whether makeup can also make her look more menacing...
Couch Gag: What will show up on the beach with Ika in the closing credits this episode?
Creepy Doll: The alarm clock doll that Eiko takes out of storage. It sits directly in the Uncanny Valley and refuses to leave. Even Eiko gives it away at the end, for its broken friend scares her even more.
Credits Running Sequence: season 2's ending has Ika walking on the beach (while the first season was static with her watching the ocean), and there will be some event from the episode that makes its appearance in the sequence. The ending of Episode 6 replaces Ika with Mini Ika.
Cry Cute: Ika-chan was weeping for a paper hat that looked like a dead squid as it flowed out into the ocean... the family just didn't have the heart to tell her that it wasn't a "comrade" of hers.
Cut the Juice: The Squid Girl robot made by Mr Tokita, Harris, Clark and Martin has its power source cut off when Nagisa trips and disconnects the cord. Luckily, they were prepared enough to have an emergency backup through auxiliary power ... by a pedal-powered generator.
Cute Squid Girl: Ika Musume herself. It's hinted there may be others around with a similar background.
At the volleyball tournament, the scientists show off their newest gadget: an incredibly hard ball, designed to be completely impossible to receive. Which means it's also impossible to serve.
Ika manages to "conquer" the local high school by tying up the principal. She then commands the students to be her soldiers so she can conquer the world! Unfortunately, the only thing she has planned after she conquers the world is...eating as much shrimp as she likes. Which she already does anyway.
Draco in Leather Pants (In-universe example): During a stage play Ika gets the crowd to cheer for the villain (a squid monster) instead of the hero like the makers intend.
Dream Sequence: The Mini-Ika episodes turn out to be these, the first of Sanae, and the second of Goro of all people.
Dynamic Entry: Flawlessly performed by Eiko to stop Ika's invasion of the school.
Easy Amnesia: Ika gets this in Chapter 106 (Season 2, Episode 7.2 in the anime) by falling down the stairs. She gets better at the end of the chapter by trying to remove her hat.
Episode 11. Ika gets her ass kicked by a creature without legs.
In the first segment of the second episode of the second season, Ika tries to play soccer, but she can't even do the simple act of kicking the ball! In fact, in order to win the game, her teammates make it look like she kicked the winning goal!
Even the Girls Want Her: Nagisa is a minor case; all she needs to do to attract female customers is just sweep her hair back.
Evil Counterpart: In one of the DVD shorts, Mini!Ika is attacked by Dark!Mini!Ika, a wandering squid girl who enters into the house through the open window. It turns out to be inverted. She was just looking for food, and aside from being very competitive, is actually very nice.
Evolving Credits: After the first episode, the ending credits changed slightly in each episode, featuring something seen in the episode.
Exact Words: When she sees the preferential treatment Alex is getting for being cute, Ika demands "You will treat me just like this creature!". Gilligan Cut to Chizuru putting her on a leash.
It's shown in chapter 76 that she has bad eyesight, so she's always squinting. She gets contact lenses, but gives them up when she realizes that having her eyes open all the time makes everyone else nervous.
There's also one brief exception in season 1 when Chizuru gets an idea and her eyes open right before the scene cuts away. Though only the viewer sees this.
Face Your Fears: In Season 2, Episode 11.3, Ika overcomes her fear of Chizuru, accidentally ticks her off again, and gets dragged by her to a room whileshowing NO signs of fear.
Ika: Oh? About what? (while being dragged by Chizuru to a room)
The Faceless: Ayumi is an interesting twist, bordering on double subversion: she's not always seen in an Ika Musume mask, but she displays less of her personality when she's not wearing it.
Fanservice: Appears to be actively averted. The show takes place on a beach and has a largely female cast, yet none of the main cast are shown in a suggestive way — just a few side characters in bikinis now and then. It's rather refreshing.
Here's Ayumi. Fanservice is still rare and not the focus.
Fertile Feet: Or, rather, fertile ink. Ika Musume's ink had accelerated the growth of her melon plant to such a degree that after a week, they covered the whole house of the Aizawa family!
Feud Episode: Season 2 Episode 12.2: Isn't That A Festival? Ika and Eiko have a falling out and the rest of the sequence focuses on their making up. It's also the season finale.
Flanderization: While Ika is usually portrayed as intelligent, but easily distracted (because of her curiousity about life on the surface world), season 2 seems to have started making her more Keroro Gunsou-like. For instance, in episode 9-2, Ika is blatantly portrayed as Completely Missing the Point of using a bag and planner.
Flash Step: Chizuru demonstrates this ability when angered by Ika in Season 2 Episode 11.
Flat Earth Atheist: Squid Girl doesn't believe in ghosts, even though a horde of them helped her find her way out of a graveyard once. Her belief is justified in that she didn't even know what a ghost was at the start of the episode, so she thought they were just weird-looking humans.
Follow the Leader: to Keroro Gunsou, down to having Expies of Fuyuki, Natsumi and Aki. And a Verbal Tic, de arimasu. Interestingly, Keroro sometimes features an underwater civilization that could execute a far more effective invasion if need be.
Freeze-Frame Bonus: Season 2 Episode 5 Part 2 - Kiyomi's 'hidden' wish is never said out loud, but the camera briefly shows it to you before she snatches it away and destroys the wish. It's for a bigger bust.
Genius Ditz: Ika Musume is able to use a cellphone and camera without reading the manual or hearing an explanation on what they're for or how they work. She's able to perform high-level math as well without batting an eye, not to mention being able to pick up Japanese (and later English!) in minutes. She's also one hell of a drummer and baseball pitcher too. So far (much to her annoyance), invading is the only thing she really sucks at.
Humans Are Bastards: Alluded to; when you think about it from her perspective, Ika Musume's so-called invasion is quite justified when you have to watch your loved ones literally choke by our garbage every day.
Or the fact that Japan is well known for overfishing their waters. That said the show is more Humans Are Flawed: everyone is good, they just shouldn't dump trash in the water. Part of Ika's character development as the show goes on is her own realization of this.
Hurricane of Puns: In the inklish dub, Ika sbeaks almost entirely in puns. If there's efin the smollusk chance of her kraken a "fish" or "squid" pun, she'll do so.
Idiosyncratic Episode Naming: All the episode/chapter titles are in the form of questions, ending with, in Japanese, "-nai ka", which signifies a question in the informal mode, with the "i ka" in katakana for emphasis. This makes for a pun with "ika", which by itself means squid.
Idiot Ball: Cindy carries it for a little while in S2 4.1 when she fails to realize Eiko is still speaking Japanese instead of English and the In My Language That Sounds Like phrases get more and more ridiculous. It's still hilarious though.
I'm Taking Her Home with Me!: The beginning of "Won't You Keep It?". Sanae tries to do this on a regular basis to Squid Girl, but always gets punched away.
Innocent Fanservice Girl: Averted. Sanae wanted Ika to be this, and was very disappointed to discover that, yes, she does wear something under her dress. And not even panties: she wears a modest one-piece swimsuit so that nothing is exposed when Sanae gets a peek.
Insane Troll Logic: In episode 10.2 of Season 1, Sanae attempts to get rid of her obsession with Ika. Although it's hard, she seems to manage to do it, and starts to act somewhat normal around Ika. Near the end of the episode however, after Ika greets her normally, Sanae reasons that Ika greeting her must mean she really wants her instead. Which then causes her to then attempt to do The Glomp on Ika, and causing the latter to resume hostilities towards her.
Instant Expert: Squid Girl/Ika is able to do complex math and speak English with little more than a quick glance at the books. Which annoys Eiko to no end, as it's difficult for her to pick up either subject.
Insult Backfire: Calling Ika "fearsome" and "dangerous" is exactly what she wants. This makes her attached to Nagisa, which only scares Nagisa more.
Leaning on the Fourth Wall: In Episode 10 of Season 1, Ika Musume draws each of the characters. When Takeru takes his turn trying to draw Ika Musume, his drawing looks exactly like her, but he complains that his drawing looks sort of like a manga or an anime...
Light 'em Up: Like certain species of squid, Ika's able to make herself luminous.
Loophole Abuse: In one episode, Ika plays soccer with some of Takeru's schoolmates. However, she doesn't know how to play, and when she's told she can't use her hands, she resorts to using her tentacles instead, which to the kids still looked like she held the ball in her "hands".
Love Dodecahedron: Sanae loves Ika, who loves Nagisa (in a terror-inducing kind of way), who has a crush on Goro, who is in love with Chizuru.
And then Kiyomi and her friends enter the picture, too.
Eiko: I don't even want to imagine the relationship map for this.
Machiavelli Was Wrong: Inverted in that Chizuru is able to keep Ika's world-conquering ambitions down simply by looking at her. It's supposed to be a comedy/slice-of-life series, so it doesn't focus on the fact that Chizuru is controlling Ika through fear alone.
Mad Scientist: Cindy's colleagues. Ayumi's father has several Mad Scientist traits, too. He eventually teams up with them to build the ultimate robotic Ika Musume, as seen in Chapter 181 (Season 2, Episode 11.2 in the anime).
Mundane Object Amazement: Being an invader from the sea, this is to be expected. Especially in the last segment in Episode 8.
Mundane Utility: Ika possesses ten tentacles with super strength, super speed and super dexterity. They come in really handy in her job as a waitress. Oh, and the squid ink she can produce makes a formidable pasta sauce.
Ika has a white hat that resembles a squid's head, but it may be more than that. Episode 6 states that if it is detached from her head, she'll die.
It's shown that she really WILL die if it's removed in Chapter 106 (Season 2, Episode 7.2 in the anime) because, for all intents and purposes, it's part of her skull. She tries to forcibly pull the hat off, which works about as well as a human trying to tear off his own scalp. Eventually she creates a small rip, the shock of which was enough to clear away her Easy Amnesia.
She wears a more conventional Nice Hatover her squid hat in Episode 3.1 of Season 2 (Chapter 167 in the manga, which also shows the MIT trio wearing UFO hats).
No Dialogue Episode: Episode five's third short is, except for a short dialogue between Sanae and Eiko, a single line of narration, and a few "geso"s, done entirely without dialogue. This makes the entire short ten times more effective than it would otherwise be.
The supposedly sweet big sister Chizuru is good at inducing these moments in people.
Nagisa on first seeing Squid Girl.
Ojou Ringlets: Ika acquires these after one of her makeover sessions.
One Dialogue, Two Conversations: Ika and Goro both consider themselves "protectors of the sea", and thus form an uneven alliance, as their motivations (world domination vs. saving people) are rather different.
Only Sane Man: Nagisa considers herself to be this, seeing as she's the only one in the whole beach to consider Ika-chan as actually threatening. Understandable, as she's never seen Chizuru in action (she finally does at the end of episode 9, and her reaction is what you'd expect). Narratively, though, Eiko fills the role more obviously; she's incredulous about Ika's origins at first, she's often the one who has to rein the other characters in (Ika and Sanae in particular) and her only "quirk" is her hot-ish temper (and really, given how Ika acts, can you blame the poor girl?)
Literally. Takeru pretends to be Squid Boy with a disguise consisting of a paper hat and coloured strips of paper. Ika falls for it. Even when it's removed.
Chizuru in episode 12 after Eiko crashes into her. She then switches places with her and dons a wig and the Noh Mask Rider Hannya mask — with her real hair hanging out quite obviously.
Parental Abandonment: Chizuru, Eiko and Takeru are siblings and live together, but their parents seem to be nonexistent. So far it has not been mentioned if they are away or dead, but Chizuru says in the fifth volume of the manga that nobody uses their bedroom anymore. They appear in a Happy Flashback Eiko has in Chapter 79 (Season 2, Episode 9.3 in the anime), which makes her cry.
The Peeping Tom: The burglar from Season 2, Episode 8.1 (Chapter 127 in the manga) was captured because Sanae saw him through one of the surveillance cameras she had set up at the Aizawa residence without them knowing.
Poor Communication Kills: Eiko in Season 2's episode 4.1, where she unintentionally insults Cindy, and later scares off an English speaking guy due to her use of Japanese which sounds like English words.
Pungeon Master: Ika/Squid Girl herself; this is exaggerated in most translations and the English dub. She doesn't do it on purpose so much as she actually thinks that's how things are pronounced. Eiko and the others quickly notice it's part of her mannerisms.
Razor Sharp Hand: Chizuru has this ability, but only demonstrates it on Squid Girl's tentacles.
The restaurant is located on Yuigahama beach in Kamakura.
In both the manga (Chapter 147) and the anime (Season 2, Episode 6.1), they visit Kamakura's Daibutsu.
Recycled In SPACE: Inverted. This show is basically Keroro Gunsou without that pesky "space" thing... Also, Squid Girl's presence is public knowledge.
This anime can be considered as Japan's own Spongebob Squarepants, with the setting taking place on land and most of the creatures being replaced with humans. Except for the whole "becoming a network's cash cow and extending it for a bazillion seasons" thing.
Ika Musume herself can be considered as Japan's gender-flipped and moefied Squidward Tentacles.
Reed Richards Is Useless: In their pursuit of extraterrestrial life, the MIT scientists have cured cancer and created a universal translator. Unfortunately, in their single-minded pursuit of the bizarre, they don't give a crap about either of these discoveries.
Relax-o-Vision: In Season 2, Episode 8.3 (Chapter 156 in the manga), Ika suffers a heat stroke and can barely move. While she imagines what Sanae could do to her in that incapacitated, defenseless state, we are shown this instead. Fortunately for Ika, Even Sanae Has Standards, and she actually refuses to take advantage of the situation.
And Season 2, Episode 2.3 (Chapter 166 in the manga) reveals she can "fly" anyway.
Required Secondary Powers: It's eventually explained that the whole reason Squid Girl can pick up people and other heavy objects with her tentacles without losing her balance is that she can alter her weight with her bracelets, becoming heavy enough to anchor herself.
Ridiculously Cute Critter: Mini Ika Musume in 5.3 and 10.2; both are products of Sanae's imagination. She appears again in Season 2, Episodes 4.3 (as a product of the imagination of Ika herself) and 6.3 (as a dream of Goro, who doesn't understand why).
Series Hiatus: Season 2 barely started before the show had to be placed off the air for two weeks, citing "a situation with the studio", to the disappointment of many.
Worth noting: Two of the TV networks broadcasting the second season started two weeks late and did not go on hiatus at all; the overall effect was that the subsequent episodes premiered on the same day on every station.
Serious Business: Season 1, Episode 12's volleyball competition gets particularly heated, culminating in Chizuru stepping in as Noh Mask Rider Hannya to literally meteor smash face.
When the scientists accidentally turn the store invisible, they bring about the wrath of Chizuru. They try to protect against her attack by shielding themselves. Harris erects an AT Field, Clark brings out Link's Master Shield, and Martin throws up a tortoise shell. Naturally, none of them work.
Perhaps her martial prowess is a shoutout in itself? Cutting flies and tentacles BAREHANDED? Sounds supiciously like she is a Genyu Ken practitioner.
In episode 11.1, Eiko brings a doll out of storage because it's picking up in value as a collectors item. It was part of a pair of doll toys known as Johnny & Depp.
In the background of Takeru's elementary school classroom, you can see Aho, Sethi, and Ullman's seminal computer science book "Compilers: Principles, Techniques, and Tools" (first edition). The other books on the shelf are apparently also computer science books.
The season 2 OVA has Eiko and Ika playing a game clearly based off the original Super Mario Bros., with them as the main characters. Eiko's game is even called "Super Eiko". And the game system itself is pretty much a Game Boy Micro. And in the beginning, the mad scientist trio is playing a DS game similar to Mario Kart.
In the opening sequence there is a reference to 8-bit console RPGs, perhaps specifically the second or third Dragon Quest games. A sprite that resembles Ika disembarks from a boat, enters a cave, and opens three treasure chests (there's shrimp inside, of course). A console that looks a lot like an off-colour Sega Mega Drive/Genesis can also be seen near the end of the opening sequence.
The first part of Episode 11 also features a pair of dolls called Johnny & Depp.
Season 2, Episode 5.2: One of the aliens imagined by the Three Stooges is actually "Paranoia", a boss from Space Harrier II. At this point it seems safe to assume that the makers of the anime are big old school Sega fans.
As more confirmation of the above, Season 2, Episode 7.2 shows Ika playing Golden Axe.
Smurfing: The Crunchyroll subs use this with "squid" (and give her exclamations like Squidzooks, holy tentacles, and many others) to try and convey the rather punny nature of the titles and Ika's speech.
The English dub takes this to an extreme propensity for ocean life puns. Words like "Squidy", "Krakken", "Tentacular", "Kelp", "Gilly", "Ink", "Clam", "Beak", "Jet", and numerous other words will find their way into Squid Girl's regular vocabulary. Even when you can tell the context is meant as a swear. For example, Squid Girl never says "Invasion". It's always "Inkvasion".
This also extends to most of the characters themselves, such as Sanae tearfully letting her obsession with Ika go, only to revert right back to it before the end of the episode. And later Ayumi learns to be more confident thanks to a pair of brass knuckles Chizuru let her use (causing men to be really fearful of her), only to have her dad immediately shoot her confidence right back down towards the end of the episode.
Tanabata: Ika tries to exploit it for as many wishes as she can. Kiyomi doesn't tell anyone, but she wishes for a bigger chest. In the end, Ika ultimately decides that after she finds out that some people (Chizuru, Sanae, Cindy, Harris, Clark, and Martin) wish that they have her, she wants to be safe.
Tentacle Rope: Ika does this to Eiko when she wanders into Eiko's room and falls asleep there.
Teru Teru Bozu: These and Ika's art skills are the focus of episode 10.1.
Ika is not afraid, because, not being raised in human society, she has no idea that she's supposed to be scared. Goro, however, is terrified.
They take another one in chapter 100 with the party consisting of Eiko, Ika, Nagisa, and Cindy, this time in a tunnel instead of a graveyard. Unfortunately there are a whole lot of problems with this venture (Eiko insisted on taking only one flashlight which runs out of batteries, Ika Musume's light is too bright, etc.) so they call it off. Only problem is, Cindy's missing. Cue Cindy surrounded by ghosts. Cue Color Failure for everyone else.
Three Shorts: This is because the original manga is basically a "gag-a-day" comic, with very short chapters (usually less than ten pages long).
Throw the Dog a Bone: Ika's "takeover" of Eiko's high school is the closest thing to actual invading she's accomplished. Though it also reveals that she hasn't thought through what she intends to do after her invasion succeeds.
Tickle Torture: All of chapter 81 (Season 2, episode 4.2 in the anime). Ika is eager to take it to extreme levels, but forgets that conquering humanity with tickling doesn't work if you're more ticklish than everyone else.
She doesn't realize this until she attacks Chizuru, of all people — only to be told "You missed my weak spot."
She already used it on Eiko in episode 7, as well as Cindy and the MIT trio in episode 11 of the first season of the anime, so this has become an Adaptation Induced Plot Hole.
Time Skip: In the final episode of season one, a year passes after Ika "returns" to the sea. Of course, she comes back.
With her tough, competitive attitude, playfulness, how well she gets along with Takeru compared to the other girls, and her general silliness, you could argue Ika herself acts more like a boy than a girl.
Tonka Tough: The legendary toughness of Nintendo, err... Mintendo products get referenced a couple of times in the manga. The first was when the three idiots express surprise that they accidentally broke a DS, causing them to create an even tougher portable gaming system. The second was when Cindy tries to break a Family Computer in frustration, only to stub her toe in the process without damaging the console.
Unusually Uninteresting Sight: None of the customers of the Lemon Beach House seem to mind getting served by a half human / half squid hybrid creature which carries their food and drinks with its tentacles.
Verbal Tic: Ika frequently ends sentences with "de geso" ("geso" meaning "squid tentacles" in culinary terms) and "janai ka".
And in episode 12 she changes it to "dawa".
In the dub, she loses her squiddy mannerisms, and "dawa" is changed to "You Know?" Lampshaded by Eiko later in the episode.
Goro's not afraid of near-drowning — as a lifeguard, he takes risks regularly — but he is absolutely terrified of ghosts. Although it takes a lot to get him to admit it in front of Chizuru.
Wingding Eyes: A common reaction of both Cindy and Sanae to Ika Musume, and a common reaction of Ika Musume to shrimp.
Work Off The Debt: Even after the wall is repaired, Ika will still have to work 5 or 6 years to pay it off. She did find a large bill, but Chizuru persuaded Ika to use it on a shopping trip, keeping her in Lemon's employment.
Ika: "What kind of lame wage are you paying me, de geso?"