Above the Influence: But just barely for Shougo. In episode 3, both Miyabi and Konoe feed him various supplements to boost his virility, then they spend the night with him in his bed, to "train" him to only like girls after mistaking him for being Ho Yay with Mizutani.
Absurdly Powerful Student Council: Rinka cracks down on things she deems immoral after Shougo's sister makes an announcement over the school's public announcement system, while some prominent business officials were visiting. She also makes him the morality officer, although he doesn't seem to be doing the job very well considering the girls are wooing over him still.
Accidental Pervert: Shougo is prone to these due to all of the teasing the girls like to do to him, such as when Miyabi intentionally lifts her skirt up in episode 8, then a gust of wind blows through the area.
A Date with Rosie Palms: Implied to be done by Shougo in episode 5 when his sister calls him and tells him that he shouldn't be staying up so late doing such naughty things. He doesn't outright deny it, saying he doesn't do that every night. And in the beginning of episode 9, he seems to be doing this, until the camera pans out to reveal his entire body, and shows that he was simply exercising on his bed despite his suggestive grunting.
And Now You Must Marry Me: Mizutani suggests this to Shougo as a means to resolve his issue of not knowing which girl is his sister. He immediately rejects the idea.
Arranged Marriage: Rinka is stuck in one, and doesn't seem very happy about it, as she's not interested in the guy her family set her up with but can't go against it because it's for business purposes.
Balanced Harem: So far Shougo doesn't seem devoted to one particular girl, but Konoe and Miyabi seem to have a slight lead over the rest.
Barbie Doll Anatomy: Happens briefly to Miyabi in episode 10 shortly after she's done taking a shower.
Bishie Sparkle: Mizutani has this around her when she's walking home with Shougo in episode 2. Since she's supposed to be a guy, the fact that she was clinging to his arm the entire way home made some of the students suspect they were gay.
Black Mail: Shougo's sister in episode 7 makes a broadcast over the school's PA system telling him not to find out who she is, or she's going to reveal secrets which she says are best left undiscovered.
Only it wasn't directed at Shougo but at Genda, the head of the board of directors, as Rinka tells him in episode 8.
The title of episode 6, "Cat-ear Maid Sisters", is self-explanatory. Konoe and Mei spend most of the episode wearing electronic ears and tails that respond to emotions.
Censor Steam: Rather than steam however, they darken the areas where Konoe's skirt lifts up in episode 6.
Chekhov's Gun: A subtle one, but In episode 1, while hanging out at the park with Konoe, Shougo is introduced to the clock and the distinct music it plays every half hour. This is what helps him find Konoe when she goes missing in episode 4, as it plays in the background when she calls him to say goodbye.
Its used again in episode 5 and 6, when Shougo spots Mei's phone which is exactly the same as Konoe's. Except in her case, she was pretending to be his sister to protect his true sister's identity from him, so as to avoid scrutiny and shame for being Shougo's illegitimate sister by their father's company and family.
Childhood Marriage Promise: Shougo did this with Miyabi when they were kids in the hospital, and she's held him to that promise ever since he transferred to her school. Cue shocked reaction from both Shougo and Konoe.
Clingy Jealous Girl: After seeing Mizutani getting a bit too friendly with Shougo in episode 3, both Miyabi and Konoe both go to great lengths to make sure he's not batting for the other team. He ends up running away from both of them at school as a result of this, and they both invoke this trope again when they accuse each other of trying to get ahead with him in a relationship.
Both girls display this trope again at the end of episode 4, and agree to pursue Shougo fairly this time around, much to his chagrin. Cue more Fanservice as both of them again wake him up wearing little clothing...
Every single one of the main girls in episode 9 once they find out that Yuzurina is his sister, and all of them make claims as to why they should be taken to the social party that his mom set up for him, and tells him to bring a date.
And even Yuzurina isn't above this trope in episode 9, as she spots one of Mizutani's hairs on his floor, then sniffs his bed to find the scent of a woman on it. Later, she listens in on Konoe's Fantastic Arousal and slams the wall when she thinks they're taking it too far.
Shougo invokes this in episode 6, when he tells Mei that he wants to know who his sister is in order to protect her and acknowledge her as his sister.
He does this again in episode 8, after Rinka tells him about her Arranged Marriage, which she doesn't want, because she believes in marrying for love. He suggests that they pretend to be lovers so that her family would be forced to break off her engagement, and can then choose whoever she wants to really marry. Unfortunately for him, she doesn't want to pretend...
Distracted by the Sexy: Miyabi deliberately invokes this in episode 8, when she arrives at school wearing a skirt that seems a bit too short, and forces Shougo to measure it. But she keeps teasing him and asking if he wants to look up her skirt, to which he hesitantly says no. Konoe then arrives, and demands he measure her skirt as well. Then a wind gust blows through, and both girl's skirts are lifted. Shougo claims he didn't see anything, but then he mentions Miyabi wearing shorts, which angers her because that meant he looked up her skirt when the wind blew.
Does This Remind You of Anything?: When Konoe is cosplaying as a cat maid in episode 6, her tail is acting erratically, and Shougo tries to help her with it. But as he rubs and pulls on the tail, Konoe seems a bit too excited by it. Oh, and Episode 9 too, where Shougo and Konoe make weird sounds during the beginning when Shougo was exercising and near the end of the second half where Shougo tickles Konoe unless she leaves his bed.
Double Standard Abuse Female On Male: Despite it being a total accident thanks to Mana, Shougo gets a roundhouse kick to his head from Rinka in episode 2 and again in episode 8 only he gets slapped instead.
Both Shougo and Tanaka get hit by Kotori-sensei's swimming board in episode 9.
Early-Bird Cameo: Yuzurina can be seen with the board of directors visiting the school in episode 7, but we're not given any indications that its her other than a subtle smile towards him. It's also unusual that her hair is black in that episode, but then is brown in episode 9 when she reveals herself to him. Although it could be that she was trying not to seem too obvious to him and simply dyed her hair at the time.
Evolving Credits: After episode nine, Yuzurina replaces Shougo's sister's silhouette during the opening credits. She is also among the girls during the next episode preview at the end.
Exhausted Eye Bags: Happens to Shougo in episode 5 due to his "sister" calling him almost every day at 6am. Both Konoe and Miyabi notice he's tired, and do various things to try and wake him up.
Eye Catch: It features a toy dispenser which pops out a Super-Deformed version of one of the main girls in the series. Episode 9 adds a new girl, Yuzurina Houshou, who also claims to be Shougo's little sister.
Face Palm: Shougo does one in episode 9 after Yuzurina asks him which girl he's going to bring to the party his mother is inviting him to. Naturally she brings it up when all of the main girls are with him, so they fight amongst themselves as to which one he's bringing.
Fanservice: Quite a bit of it, since it's a Harem show. Pretty blatant in the opening intro song.
Forgotten Childhood Friend: Konoe AND Miyabi. Justified, as he got hit by a car saving Konoe, which caused his memory loss, as well as strife between their fathers, which caused them to not be able to see each other again for a while. Then while recovering at the hospital, he met Miyabi there while her father was getting check ups, until he no longer needed them, and they were separated again until high school.
Friendly Tickle Torture: In episode 9 after Shougo eats dinner Konoe makes for him, she says she's dessert and won't leave his bed until he "eats" her. He then starts to tickler her in an attempt to get her off his bed.
Gecko Ending: The anime stops early with Miyabi as Shougo's sister. In the novels, however, things progress and end up a fair bit more complicated than that. Miyabi is actually his cousin and Konoe was the illegitimate daughter, but they later discover that she's not blood related to Shougo (since Shougo isn't blood-related to his father), and then Miyabi's father marries Shougo's mother, with the end result being Miyabi as Shougo's step-sister and Konoe as his lover.
Genki Girl: Mana Tendou, the student council president.
Genre Savvy: Played straight at first with Miyabi. When Konoe pretends to be Shougo's little sister helping him to change clothing, Miyabi calls her out on it, saying that only in a fantasy world would any guy be turned on by his sister helping him with changing clothing. Then she hilariously subverts it with an Imagine Spot of finding his boxers and wearing them to sleep. Shougo is understandably not too impressed by either girl's moves on him.
The Glomp: Mana does this to Shougo after he's done dancing with Rinka. Miyabi does them in later episodes as well.
Hot For Teacher: One of the male students, Tanaka has shown to have an obvious crush on his teacher Kotori-sensei. Which every time he vocalizes it, causes her to hit him with something.
Imagine Spot: Shougo has one in episode 5 about marrying Konoe.
Informed Ability: The School President is been said to be serious when it comes to her work but will act childishly when having fun. So far every time she is on screen she is just acting childishly.
Innocent Fanservice Girl: Mizutani is unaware of how babies are made, and after Shougo hands her a pamphlet on how it's done, she immediately wants to "practice" it with him. Then Miyabi and Konoe walk in on them as Mizutani is on top of him in bed. She cranks it Up to Eleven in episode 7, stretching out while wearing nothing but a towel around her shoulders. While Shougo is still uncomfortable around it, he seems to less offended by than he originally was.
"Onii-chan" means big brother in Japanese, "Senpai" is an honorific lower grade students, such as freshmen, use for higher grade ones like seniors
by the freshmen girls in episode 6.
Insult Backfire: In episode 3, while both Miyabi and Konoe are pulling the "little sister" act, he begs Mizutani for help. Both girls reject it, claiming that if Shougo looks at Mizutani, he'll get "him" pregnant. Mizutani says that "he" wouldn't mind that, to the shock of both girls, who then drag him out of the classroom.
I Thought It Meant: When Shougo asks for a DNA sample from Konoe's "mucus membrane" in episode 7, she's hesitant at first, but eventually relents, saying If It's You, It's Okay. She then bends down and proceeds to drop her underwear, prompting Shougo to clarify that he just needed it from the inside of her cheek. Cue Konoe's face turning beet red.
Little Sister Heroine: Deconstructed; Shougo wants to get to know his sister (and protect her from his disapproving family) but not in that way.
Love Confession: Rinka does this to Shougo (naked, too) when she wants to have a real relationship rather than the fake one so she could get out of an Arranged Marriage.
Love Hurts: Miyabi doesn't seem very happy in episode 9 when she sees Shougo about to kiss Konoe.
Manipulative Bastard: Yuzurina aka Denno Nayuri, although being an actress, she puts on a largely good act until things start to unravel around episodes 11 & 12.
Mistaken for Gay: Shougo in episode 3 when Miyabi and Konoe both walk in on his apartment while Mizutani is on top of him in bed. They go to ridiculous lengths to make sure he likes women, such as waking him up in bed, making him food, and later, taking a bath in his apartment, as well as snuggling up to him. The girls accuse them of this again in episode 12.
Moment Killer: Miyabi spots Konoe and Shougo sitting on a bench together at the end of episode 4 in the park, right as it seemed the two were going to kiss. She then goes into Clingy Jealous Girl mode, and wonders why Shougo had her running around looking for Konoe, just to find them spending time alone together. She also accuses Konoe of cheating to try and get ahead of her with Shougo.
Mizutani calls Shougo in episode 6 just as Mei was beginning to slowly undress herself in front of him to ask him to look for her hat which she forgot at the cafe earlier. He doesn't find it, but it stops Mei from attempting her advances on him, and it turns out Mizutani had her hat, and simply called him to interrupt what Mei was doing. Shougo then wonders if Mizutani had cameras spying on him in there, to which she neither confirms nor denies.
Shiga walks into the student council office in episode 8, just as Rinka was nearly naked and on top of Shougo, and was suggesting they become real lovers.
When Shougo was about to kiss Konoe in episode 9, Miyabi just happened to be walking within the vicinity. She doesn't say anything and hides immediately, but it was enough to stop them from kissing when Shougo thought he saw someone in the area.
Parental Abandonment: Miyabi reveals to Shougo in episode 12 that her mother left her and is only seen rarely nowadays. Also played straight with her father, which from the Flash Back of Miyabi's childhood, shows that her mother didn't want anything to do with him, even going so far as to not spend the money he gave to help raise Miyabi.
Petite Pride: Miyabi, after she concludes that maybe Shougo would rather see small breasts like hers rather than big ones like Konoe's.
The Plan: In episode 5, after the previous episode established that Shougo's calls from his little sister are actually from Konoe, he receives more calls everyday at 6am from a girl claiming to be his sister. As a result, he was tired at school, and took naps in Mei's secret room at school, and also learned more about Mei's cafe shop and how it used to belong to her mother. Then he learns from one of the girls working there that Mei was selling it and moving to America, so he confronts her about it in episode 6.
Turns out that Mei's shop was just barely scraping by, so Shougo decided to help her pick up some business. And does a fairly good job at that. Then Mei starts hitting on him rather aggressively, suggesting they get married and have a "superior" kid with both good business and Moe traits, which understandably turns him off, as he suspected Mei may be his sister after all.
But in reality, Mei was merely pretending to be his sister, and when he turned her down, she would then use her failing business as a pretext for leaving. But then he threw a Spanner in the Works by turning the business around. Turns out that Mei knows his sister's identity, as they played together as kids, and Mei put on the act to prevent Shougo from finding out who she really was, to avoid the scrutiny, public scorn, and shame that the Mikadono group would no doubt heap on his father's illegitimate child once her identity became public. So she initially refuses to tell him his sister's identity. But Shougo insists on knowing, so that he can acknowledge her as his sister, as well as protect her. Mei is still cautious about it, so she wants to make sure Shougo can back those words up first.
Red Herring: Apparently nothing before episode 9 had anything to do with Shougo's mysterious little sister.
Another large one occurs in episode 10 regarding the DNA test. Although it says he's blood related to Yuzurina, later in the episode Yuzurina is wondering if Mei and Miyabi are good friends since Mei seemed really worried about Shougo taking advantage of the girl while she was passed out. Then Shougo begins wondering when Mei and Miyabi became really good friends. See The Plan for more information.
Relationship Upgrade: Invoked at the end of episode 8, with Shougo suggesting it to help Rinka break off her engagement with one of her family's business partner's son. Although he only meant to pretend it so that she would then be free from the engagement, and therefore able to choose whoever she wants, Rinka is more than happy to apply the trope to them, and takes off most of her clothing so they can become "real" lovers, instead of just pretend ones. Later, she brings him a huge lunch, and says that her father approves of him dating her, as well as an eventual marriage, much to his shock. Cue an enraged Konoe and Miyabi who demand to know what exactly happened, as the camera pans up while Shougo screams.
The Reveal: In episode 4, after Shougo tells Konoe about what happened between him and Miyabi from episode 3, she realizes she went too far with the little sister phone calls. She then tells Shougo that she's not his sister, and knew him from childhood, and he saved her from getting hit by a car, hence the injury to his forehead. While Shougo is glad that the phone calls weren't from his actual sister, he still wonders who showed up at his father's funeral that day.
Miyabi also delivers one to him shortly after. She played with him at the hospital when her father was getting check ups, fell in love with him there, and they often pretended to be married. So when he transferred to her school, she was happy to see him again.
Mei gives one to Shougo in episode 6, after he finds out certain things. See The Plan.
Scars Are Forever: Shougo has one on his forehead. Apparently, he got it after he was hit by a car when he was younger.
Schmuck Bait: When Shougo's "sister" calls him in episode 3, she tells him that she'll reveal who she is if he says that he'll marry her ten times. When he refuses, she says "I love my little sister" ten times would suffice. Cue an initial refusal from Shougo, who gets a disgusted face, then does it, after which the girl says she's going to have sweet dreams now and then hangs up on him.
Shougo asks all of the main girls this in episode 9 to keep his sister's identity a secret after she reveals herself. Or so he thought.
Miyabi has one as well, which she tells Shougo about in episode 12, that she's his real sister, and wanted to tell him but got nervous about it. It wasn't until Yuzurina showed up which then forced her to play her hand in revealing it.
Sensei Chan: Maiko Kotori, Shougo's homeroom teacher who looks and sometimes acts like she's younger than the rest of the girls.
Sexy Discretion Shot: Used quite heavily with Mizutani, since she likes to exercise in Shougo's apartment naked.
Skinship Grope: Miyabi does this to Konoe at the pool in episode 9 after the two girls exchange insults regarding their bodies and the way it affects their swimming.
Smarter Than You Look: Shougo, despite being depicted as a normal high school student, he has been able to deduce many things on very little evidences and comments he hears.
Squee: Random high school girls do this in episode 6 when Shougo and Mizutani both dress up like butlers and are serving/taking pictures with them.
Stalker with a Crush: Shougo hears a girl's voice in the first episode who claims to be his long lost sister. She proclaims that she's going to marry him, and will usually call him and tell him she saw what he was doing earlier that day/episode.
He hilariously wants this trope to be invoked in episode 3 when both Miyabi and Konoe are sleeping next to him in his bed, to confirm that one of them (or neither one) would be his sister, but unfortunately for him, she doesn't call that day.
Stop Helping Me!: Shougo runs away from Miyabi and Konoe in episode 3 due to their insistence on "training him to like girls".
Sweet Polly Oliver: Mizutani Ikusu, aka Mister X. Revealed within minutes in the same episode (as well as the opening), and Shougo initially thought she really was a man during their first encounter. She claims to be doing this under the guise of discovering which girl is his sister at the school, but Shougo wonders about her tactics at times.
Troll: Turns out that in the early episodes, the girl claiming to be Shougo's sister was actually just Konoe screwing with him. And she seemed to really be enjoying it, up until he suspected that Miyabi was the one calling him and was in fact his sister, which caused her to then go into a My God, What Have I Done? moment.
Tsundere: Miyabi. Surprisingly she shows more of a Type B "deredere" than Type A "Tsuntsun" toward him after their initial meeting.
Rinka as well. When she wonders if she really acts like this, both Mana and Shougo give her a weird stare.
Unwanted Harem: Largely thanks to the fact that the girls at his school know his last name, and that he's the son of the successful business owner who died recently. And also because he's a genuinely Nice Guy.
Episode 3, when Shougo strongly suspects that Miyabi may be his sister.
Episode 6, When Mei reveals an even bigger bombshell, that she knows who his sister is, and deliberately pretended to be her, so as to keep him from knowing her true identity. See The Plan for further details.
Episode 9, where a new girl named Yuzurina Houshou (the girl with the board of directors during the school inspection in Episode 7) claims to be Shougo's little sister and moves to a room next to his. The rest of the girls are understandably shocked about this and they demand that the two take a DNA test to confirm her confession. The DNA test confirms it.
Episode 12, Yuzurina isn't his sister, it's Miyabi!
Zettai Ryouiki: Konoe Tsumura in her school uniform and the maid uniform.