Maken-ki!

Maken-ki! (also known as Maken-ki! Battling Venus) is an ecchi action-romance anime (with two seasons: the 2011 original and the 2014 Maken-ki! Two, plus some OVAs) based on Hiromitsu Takeda's manga.

Quick synopsis: Takeru Ooyama is your classic perverted high school guy who enrolls at Tenbi Academy, excited because the formerly all-girls school just went co-ed — meaning lots of girls and hopefully a harem-filled school life.

On his first day, he reunites with his childhood friend Haruko Amaya (who's tough, jealous, and part of the student council's disciplinary group), meets Inaho Kushiya (a cheerful girl who claims to be his fiancée), and encounters Kodama Himegami (a cute but deadly blonde who declares she wants to kill him).

He quickly discovers the school isn't normal: it's a combat academy where students harness magical/spiritual energy called Element and wield powerful crafted weapons known as Makens (or "Maken") to duel each other in school-sanctioned battles.

Takeru gets pulled into this world of fights, rivalries, and student council antics (via the elite group Maken-ki), all while surrounded by attractive girls, dealing with constant misunderstandings, jealousy, and his own initially weak/undefined abilities. The series mixes action-packed magical battles with heavy ecchi humor, fanservice, and romantic comedy tropes.

It's very much a "pervy guy in a magical battle harem school" type of show — heavy on the ecchi and lighthearted chaos, with some plot progression in the battles and character backstories over time.