Accidental Pervert: Ken ends up with Mafuyu's panties in one episode after she lost them during the school festival somehow.
Every game that Elise wants to play with Ken turns out to be very perverted two or three seconds in.
A-Cup Angst: In one of the anime episodes, Ken calls Kurimu "Pettanko" everytime she says "Stamp". Of couse he does this to make Kurimu say "Pettanko" instead. It works.
Kurimu is also quite jealous to Chizuru as well.
Aloof Dark-Haired Girl: Chizuru tends be quiet, snarky and more emotionally distant than the other girls, though it's implied that she's invoking it. Back in middle school she doesn't seem to have acted like this.
Aesop Amnesia: Played with: After seeing their own promotional video, the cast promises to actually do their jobs and become better people. One scene later, everything is back to normal, much to Ken's confusion.
Beach Episode: Does it still count as a beach episode if the cast is in swimsuits the whole time but never leaves the Student Council room?
Bittersweet Ending: The series ends with all the girls confessing their love to Ken, however due to the circumstances (The president and Chizuru being seniors are graduating while Minatsu and Mafuyu have to move away) the whole group are separated and life moves on.
Also the beginning of the DS Game, where the cast talk about the game itself.
The first episode of the second season reveals that Ken apparently wrote the Light Novels, which they give to the next student council.
Bromantic Foil: Ken, upon proclaiming himself a protagonist in an eroge, is told he's this instead.
Brother-Sister Incest: Subverted twice when Ken was "two-timing". One of the girls was just his stepsister and in the end he chose his childhood friend.
Building of Adventure: With very few exceptions, the show takes place entirely inside the Student Council Room.
Bunny-Ears Lawyer: Ken. Although for the most part he acts like a perverted idiot, he actually does care about his fellow student council and helps them out, not to mention he was able to join the student council because he had the top scores in the school. Made even more so in episode 3 when asked if the rumors that he was two-timing during junior high were true, he calmly answered yes instead of denying it, causing Lilicia to eventually give up publishing it.
Catch Phrase: "This is not a harem, it's the student council!"
Chekhov's Gag: Remember when Minatsu tried a wedding dress from the Theatre Club in Episode 1? Well, it's mentioned again in the last episode when it is revealed that Minatsu's dream is to become a bride. Cue Ken's reaction...
Minatsu brings up a good point though: Why the hell is that still back there?
Chick Magnet: So far there are only 2 female characters in this show who are not interested in Ken, one of whom never met him directly.
Chivalrous Pervert: It's implied that at least some of Ken's behavior is an act. He's shown himself quite willing to get himself into bad situations to spare the rest of the council. He does almost all of the paper work for the council just so he can create a fun environment for the girls to hang out in.
Ken: Uhh.....Oh yeah, did you all record that show from last night?
EVERYONE: WHAT'S POKKONCHO?!
But seriously, WHAT THE HELL IS POKKONCHO?!
Drives Like Crazy: Magiru only drives once to take Ken home when he is sick, but wow does she fit the bill.
Duck Season, Rabbit Season: In the first episode where Kurimu is loudly approving requests with her stamp by saying shonin ("approved"), Ken stands behind a nearby blackboard and mutters pettanko ("flat-chest"). This continues for a few seconds, until Ken switches and mutters shonin and Kurimu reacts by saying "pettanko". Once her brain catches up, she starts crying into Chizuru's generously endowed chest...
Kurimu (Rolling on the ground like a baby) "Chizuru, I hate you!!"
Dysfunction Junction: Zany antics and laughter aside, everyone in the council has some deep seated personal trauma, be it bullying (Chizuru), a broken family (Minatsu and Mafuyu) or a broken heart (Ken). It could probably be argued that Kurimu uses her position on the council to make up for her lack of physical development.
Eroge: Knowing about these is surprisingly key to the entire plot.
Expy: Ken, before joining the Student Council, was a slightly less insane Taichi Kurosu. Also, some fans think of him as K1.
Endless Game: Lilicia and Elise have one of Shiritori. They both use the mono aluminum strategy, meaning every word past the first is an aluminum compound beginning with "mu". Color my head asploded.
Family-Unfriendly Aesop: Parodied in-universe with Ken's speech that Kurimu really doesn't need to bother with fixing any of her flaws because being an energetic idiot makes her popular and attractive. It's taken to heart and freaks him and Chizuru out, so they put an end to that.
Fanservice: Usually takes place in Ken's overactive imagination, with the exception of Episode 5, or when the girls are wearing swimsuits. Also again in the game.
Gamer Chick: Mafuyu, who spends quite a lot of her time in the show on her PSP or updating some gaming wiki (and she gets really upset when Ken asks her to drop the latter in favor of getting back to work).
Hikikomori: Mafuyu, who is both a gaming-obsessed shut-in and one of the more popular students in her class. Somehow.
The latter's partially lampshaded in that she was asked to wear a tiny outfit in public, but was too socially inept to realize she was supposed to be embarrassed while wearing it. This got her enough notoriety with the student body that she won a spot on the council.
Hot Teacher: Student Council Advisor Magiru Satori. Seriously◊: a black choker, a miniskirt and Zettai Ryouikiwith visible garters? Hekiyou Academy seems to have a very loose staff dress code. Then again, Satori-sensei apparently doesn't teach any classes anyway.
Homoerotic Subtext: The main point of Mafuyu's delusions, but in episode 12 it becomes "real" along with Nakameguro!
Hypocritical Humor: Minatsu lectures Ken about not being able to recognize her with her hair in a different style, and a few episodes later they go by train to Tokyo. When Mafuyu takes her ribbon off, Minatsu is unable to tell it's her own sister.
Antenna Hair: In episode 6, after finding out that the Shiina sisters are transferring to a school on the mainland, Chirizu is playing with Kurimu's ahoge. Kurimu sits up quickly and suddenly has about eight sticking out of various spots on her head.
Kuudere: Ken comments that Chizuru's coldness will just make her sweetness more intense. She agrees: when she liked one guy, she filled his locker with reams of paper with the words "I love you" written overand overand over. Intense.
Loli Con: Ken is accused of being this when he brings Eris to this student council room.
Man Child: Kurimu is eighteen years old but has a maturity surpassed by Lilicia's little sister, Elise.
Meaningful Name: The name of each of the girls in the Council corresponds to the season in which Ken met them in; they are as follows: Sakurano (Cherry-Blossom-Field) Kurimu = Spring. Shiina Minatsu (Deep-Summer) = Summer. Akaba (Red-Leaves) Chizuru = Autumn. Shiina Mafuyu (True Winter) = Winter. These are significant as they represent the times in the previous year of Ken's life when meeting each of them gradually helped him out of suicidal self pity and depression.
Meganekko: Chizuru, part-time as she only wears glasses when doing extended reading/writing. Nakameguro offers a male variant in Mafuyu's fantasies.
He also wears them when he appears outside of Mafuyu's mind. In fact, he looks exactly the same!
Minimalist Cast: There are 5 main characters, and only about a dozen people are ever shown on screen. Ever.
Older Than They Look: Kurimu is actually an 18 year old senior at her school, and yet looks younger than Mafuyu.
Only Sane Man: While Ken does not normally fullfil the qualifications of this trope, when the student council runs a radio show he plays this trope to the T so that he would be safe for radio. He breaks down when one part has Minatsu and Mafuyu read a yuri script on air.
Only Six Faces: Well, not even six, really. I mean, there's only about a dozen different people shown. But the girls all seem to have the same face.
Neither is Mafuyu about her obvious gaming addiction.
Does Mafuyu even realize she's a geek?
Rapunzel Hair: Chizuru's and Mafuyu's hair goes well past their waist.
Rummage Sale Reject: The girls' school uniforms are pretty odd, but alright...but as for the guys? Can you say "magenta-and-black plaid slacks"? Honestly, it works on a miniskirt, but who had the bright idea to put this pattern on any pair of pants?
School Festival: The festival in question doesn't show until episode 10, but deciding on its theme is the major round-table discussion for episode six.
In the game, the scene is depending on your decision before. Seeing Chizuru and Kurimu wearing in a bunny dress while doing a race or helping Minatsu in a "Horse" Battle
Sentai: After deciding that the school festival theme of the year is "Hot Bloodedness", the council goes into a Sentai tangent, including trying to decide their colors. A reference to Tentai Senshi Sunred even makes it in.
Serious Business— Elise's cat's cradle patterns. Somehow she shows the entire cosmos using a piece of string.
Ken:I can see it! The sky's tears!
Elise:Cat's cradle is so much fun!
Ken:It's too much fun! It's beyond the fun any human can enjoy!
Shaped Like Itself: Mafuyu won't forget about Sugisaki-senpai until the day Mafuyu forgets about senpai!
Ship Tease: The famous Episode 11, seriously this episode only exists to tease all Ken/Mafuyu shippers.
Shiritori: Ken and Elise, Lilicia's little sister, play a round when she invades the council room in episode eight. This gets annoying for Ken when Elise keeps ending up at the names of rival light novel publishers.
Sleep Learning: Chizuru is seen using it on Kurimu, and the effects make themselves visible the next morning.
Something We Forgot: At the end of episode five, Chizuru gets a look in her eye that says this. Turns out that Ken is still in that locker.
Stepford Smiler: Recent chapters and episodes imply that Ken's happy-go-lucky persona is a defence mechanism to keep him from a severe emotional trauma from back in junior high, and not his actual personality.
The Atoner: After Ken's two-timing hurt his stepsister, not only did he not defend himself against his classmates' bullying, he even asked for it.
In truth, he didn't two time at all - it was mostly due to his misplaced guilty conscience. His stepsister went into depression when Ken, who she was in love with, started dating his childhood friend. The couple broke up when Ken spent more time taking care of his stepsister. He couldn't make both happy. Each of the girls in the student council saved him during his first year of high school. Joining the student council is his way of showing his gratitude toward them with the belief he can keep everyone happy this time.
The Pirates Who Don't Do Anything: Lampshaded with Mahiru, who refuses to teach. Although... she was never really given a chance to. She has about thirty seconds of screen time total so far.
Unresolved Sexual Tension: Too bad Ken, even though one of the girls has actually confessed to you she still has no intention of having sex with you.
Verbal Tic: The cast randomly assigns each other one, and runs with it. Chizuru's "Mokyu~" stands out the most.
Victorious Childhood Friend: At first played straight and then subverted: In middle school Ken was in a Love Triangle with his sister-in-law and his childhood friend. His childhood friend won, but the relationship did not end well... at least for Ken.
He starts dating her again in the novels. A bit of a Base Breaker for the English speaking fandom at least.
Who Would Want to Watch Us?: At one point, the cast tries to write a novel of their own "adventures", even though they are characters in a book. This quickly turns into a Hostile Show Takeover. Everyone has wildly divergent ideas of what they want the story to be.