Balanced Harem: Friendship is a much more important theme than romance, but as the guys' feelings deepen without a clear Love Interest on Mafuyu's part, this will be the eventual outcome.
Battle Butler: Yui Shinobu wants to serve as Miyabi Hanabusa's personal ninja...
Wakana could count too in a way, since she considers herself to be Hanabusa's bodyguard.
Becoming the Mask: Shinobu faced this problem as he infiltrated the Disciplinary Club. When he's finally asked to betray them, he ends up realising he wants to stay.
The Bet: Takaomi bets 5 years of salary that he can double the number of applicants to the school within 3 years. The real reason and reward for the bet between Takaomi and the principal are not revealed until volume 7.
Book Dumb: A great part of the cast. Subverted with Hayasaka who seems dumb in a lot of ways but actually pays attention at school. Mafuyu remarks on how meticulous his notes are or how there are no doodles in his school books.
Actually Mafuyu may take the cake in the dumb department. She's extremely proud of only having one notebook for all her subjects. Subverted, because Yui finds a way for Mafuyu to learn things very fast exactly because her head is completely empty.
Born Lucky: Gotou Daikichi, the third strongest member of Okegawa's gang.
Brick Joke: Several. Including the time Mafuyu and Hayasaka went to look for Okegawa (the school's 'banchou') in the Old School Building. They see a few cockroaches and Mafuyu instinctively squishes them with the closest possible object she could reach, which happens to be Okegawa's school bag that had been lying on the floor. In a later scene the two are face to face with Okegawa who is incidentally carrying his bag with him and they can't help staring at it. Naturally Okegawa thinks they are staring at something else.
Bruce Wayne Held Hostage: Mafuyu's status as a weak mascot girl causes this sometimes. In one, oddly subverted case Natsuo (her Secret Identity) has to escape the kidnappers to save Hayasaka who has run off to save her.
Bruiser with a Soft Center: Banchou. Probably the first and only person to cry over a Nekomata movie. His pen name is Strawberry Love for god's sake!
The Charmer/The Empath: Aki. Possessed of a near-superhuman ability to read female body language, he uses it to make them happy - whether by match-making or match-breaking - up until he runs into Komari. The outcome of that one sees Komari becoming honest with her emotions around him, and the two of them becoming an Official Couple.
Chekhov's Gun: The fortune Okegawa got in the New Year's chapter that warned him about not being late (very subtle, one needs to look closely to decipher it). In chapter 66 he is conveniently being held back a grade because he was late for his exam.
The Chessmaster: Miyabi & his father. Kousaka tries to be this, but fails miserably. May also apply to Takaomi.
Cool Big Sis: Mafuyu, while she can be silly and childish, is looked-up to by her "ex-gang brothers" and has a protective nature... She will certainly play this role to anyone who needs her such as Hayasaka, Ayaben, Aki and Okegawa-banchou.
The Cutie: Komari Yukioka, she is so adorable that some people faint from her cuteness.
Defeat Means Friendship: Happens every so often. Okegawa is the earliest and most conventional example... And given Mafuyu's tendency to help everyone it just keeps happening again and again.
Dumb Blond: Both played straight and averted with Hayasaka who is 'dumb' in many ways but not book dumb. Bonus points for being recognized as a Japanese Delinquent immediately by everyone because of his hair color.
Expository Hairstyle Change: In contrast to her gang leader/yankee days where she had dyed long blond hair, present time Mafuyu sports a short cut and her natural(?) hair color.
Facial Dialogue: Komari has this down to the point it's a virtual superpower. Since she always says the wrong thing while talking, she's developed her body language to the point she can get most anyone to do what she wants.
Hot-Blooded: Hayasaka in particular. He just loves to fight and Mafuyu/Natsuo has to use shounen manga-style power diagrams to get him to learn how to dodge in a fight (he never used to dodge his opponents' hits because he considered this to be cowardly).
Komari too; she's shorter than most of the girls, let alone the boys.
I Just Want to Have Friends: Mafuyu. She wants to be a girly girl and have actual female friends since she only used to hang around guys during her time as banchou. (No girl would dare to come close to her.) This results in a total misconception on her side on how girls act and she ususually ends up seeming like a Casanova Wannabe when trying to approach girls. Needless to say, all her attempts to obtain female friends fail horribly. Unless you count Okegawa/Banchou. The corniness totally works on him.
"Banchou" for Okegawa (even after he gets beaten by Mafuyu and stops being the actual Banchou for a while...).
Ayabe once called Mafuyu "Mafu-Mafu",
I Was Beaten By A Girl: Seeing how devasted Okegawa/Banchou was at getting beaten by a smaller guy Mafuyu suspects he would be even more devastated if he found out that it was in fact a girl that took his position as Banchou from him.
He later ends up finding out the truth, but at point he doesn't seem to care about it.
Japanese Delinquents: The cast is full of them. Pretty much everyone either used to be a delinquent, is a delinquent or is trying to quit being a delinquent.
Laser-Guided Amnesia: Mafuyu forgot about Takaomi due to head injury, and she still has missing pieces in her memory. Usually the flashbacks' of their childhood days are from Saeki's point of view.
Legacy of Service: When Wakana first meets Hanabusa and is asked to help him/look out for him, she thinks of this trope since her parents work for his parents.
Lethal Chef: Takaomi. Mafuyu is barely better than him.
New Transfer Student: Parodied. Mafuyu is a new transfer student, but she is such a Cloud Cuckoolander that everything associated with this trope is turned upside-down. She's so excited that she dons a new school uniform a day before the school starts, her well-practised introductory speech is so out-of-character that Saeki bursts out laughing, and when ordinary classmates (non-delinquents) talk to her she is deeply moved. Her Friendless Background is only her imagination; in fact, her friends from Higashi High appear from time to time and have their own sub-plots.
Paper-Thin Disguise: Played straight and lampshaded quite often with Mafuyu's 'Usa-chan man' mask and her Natsuo disguise. Also when Mafuyu does not have her mask with her and tries to mask herself by wearing her t-shirt over her head (unfortunately it has her name on it) or wearing her wallet chain and a pack of tissues as an eyepatch over one eye.
Shrouded in Myth: Hayasaka and Okegawa’s view of the previous gang leader of Higashi High, Mafuyu, is so messed up that they mistake her gender, and that’s one of the lesser wrong assumptions they make. All thanks to Maizono.
Socially-Awkward Hero: Mafuyu, hands down. Jumping through the window when tied into a chair is nothing compared to the terror of speaking to normal girls.