Jinguuji Marimo

In Extra, Marimo serves at the homeroom teacher for the class of 3-B, attended by students such as Shirogane Takeru, Kagami Sumika, and at one point, Gohda Jouji. Much to her dismay, most of the class doesn't seem to respect her all that much by referring to her using nicknames, such as those used by Takeru; for example, "Marimo-chan" rather than "Jinguuji-sensei". She has a rather ditzy sort of personality, has issues with holding on to boyfriends (she is the one to always get dumped) and is constantly bullied by her longtime friend, Kouzuki Yuuko. Yuuko also often forces Marimo to do things such as cosplay, and betting Marimo's "freedom" on things such as competitions between their two homeroom classes. She gained her nickname of "Mad Dog" during college, where she was fairly well-known to be a a bit of a frenzied drunk. If Takeru prioritized her throughout the game, he is given an extra option with her during the hot springs arc. There, the true extent of her power as a "Mad Dog" is unleashed on the helpless Takeru. During her bad ending she rapes Takeru multiple times (to the point of sexual exhaustion and beyond) and after she collapses to sleep, Takeru is fearful of his future (he says he will be forced to change schools among other things). Before he could run away however, he is dragged to floor by a smirking Marimo who gently whispers into his ears "Round Two". What happens next is left to the reader's interpretation, but considering it's a bad ending by Age, then the aftermath will have serious consequences a la Kimi ga Nozomu Eien. It is implied that Extra Marimo did in fact have romantic affections for Shirogane.