Yukie defeating Azumi and her elite maid squad and then holding off Momoyo.
Miyako defeating the entirety of the archery club on her own.
Chris defeating Kokoro while heavily outnumbered and then defeating Margit in a duel.
Momoyo breaking down a barrier specifically designed to keep her out in less than a minute, then battling the three of the other strongest fighters by herself and nearly winning before the battle gets Cut Short.
Yamato manning up and leading the suicide brigade to push for the final victory.
Gakuto defeating Jun in one punch then taking on 70 men at once with a broken leg.
Cap curbstomping every general he encounters, culminating in a final duel with Hideo that wins the war.
Gen breaking through Kyougoku's mind control through sheer willpower and defeating a Magatsu Cookie after getting repeatedly shocked with 10,000 volts of electricity.
...and that's just the Kazama family!
If you've actually played the game, the entirety of episode 1 of the anime, which recreates the Kawakami-sen (Kawakami battle) from Momoyo's route, is pure awesome. If you haven't, it'll probably just be confusing.
Ageha calling Momoyo out on the rooftop, during episode 9.
Matsukaze calling out Momoyo's hypocrisy in episode 10 also counts as well.
You'll only appreciate this if you're familiar with MajiKoi's spiritual predecessor, Tsuyokiss, but the true 4th member of the Shitenou isn't Tsubame, as in the anime, but Otome-san, the resident badass of that game! She only appears in Momo's route, and due to legal issues, her image is never used so you only hear her voice, but considering everyone who's played Tsuyokiss & was playing MajiKoi was likely wondering who was stronger, Otome or Momoyo, Otome showing up to do battle at the end of the Kawakami-sen was EPIC.
They added a lot more animation to the game's sequel, S. Many of the finishing moves in the prologue's battle with the western school were pretty cool. However, in Koyuki's route, and the climactic battle with the Ryouzanpak, every single animated finishes are made of pure awesome. Every. Single. One.
Wanko's overmatched against Youshi, and is about to fall when the whole damn school cheers her back to battle. Youshi get's weakened by Youichi's snipe attack, which allows Wanko to slide under her guard and finish with a jumpkick to the chin.
Tatsuko berserking out and literally curbstompingShishin, once she finally gets a hold of her. Then finishes her by knocking her into the air, then waiting for her to come down to smack her with her makeshift hammer.
Tsubame powering up in her satellite powered spider armor to finally knock out Seiso.
Mayucchi & Yoshitsune's ridiculous aerial sword battle that starts from the rooftops of the Kuki building, proceeds between the towers, which they use to spring back & forth, and ends up on ground level. Mayucchi finally wins with an hour-long powerup, which Yoshitsune waits for.
Koyuki & Miyako teaming up to take out Rin with a nice tandem kick. Doubles as a moment of heartwarming considering both of their backgrounds, especially regarding Yamato (at least in Koyuki's route, for Koyuki).
Culminating with the massive Kawakami-Ha battle between Momo & Hume... In Space!
The tag tournament in Tsubame's route has many of them, but one of the more unconventional ones has Cap and Ootomo defeating Margit and Chris, despite them being more skilled than they are, by destroying the stage and giving them an unexpected ring out.