|“||Yamai-san is a straight-up yandere.||”|
|Full Name||Yamai Ren|
|School||Itan Private High School|
|Manga Debut||Chapter 5|
Ren sports a long auburn hair that flyaways at the end and straight cut bangs adorned with a red ribbon on top of her left ear. Yamai on school days wears the Itan Private High School uniform while wears a more girly fashion on off days.
Ren is a the leader of the ladies group in Class-1 and like the whole student body, a member of Shouko's entourage. She calls Shouko "Komi-sama" and secretly worships her, in a different level even so she calls herself "an ordinary high school student". Ren's real self appears and attacks violently when someone else unimportant approaches Shouko, especially Tadano Hitohito who is often with Shouko. Despite her threatening on Shouko and Hitohito, through twists and turns Ren toned down her insanity and acts as a good friend of Shouko even though Shouko formerly refused being Ren's friend.
In her Second year at Itan High, Ren is shown to have made friends with Manbagi Rumiko's friends, the gyarus, in her class.
- Her name "やまい れん (Yamai Ren)" is written as mountain and well but can also mean illness which the word yandere came from. While "れん (Ren)" is an alternate reading of "恋 (koi)" which means love.
- She claims that she doesn't get along with Nakanaka, and vice versa, but the two are seen acting in sync various times. (Their classmate Sukida Lily ships "Naka x Yama")
- Her idea for the Cultural Festival was the Haunted House. With her ulterior motive being that nobody would complain if she felt up Shouko's butt in a dark classroom.
- She's terrible at apologizing. As seen when she apologized for kidnapping Tadano, where although she says sorry, she still meant what she said and says she still would've threatened Tadano.
- Ren shamelessly stalks Komi, waiting outside her house for days on end sometimes. She has a tendency to show up uninvited to events Komi had arranged with her other friends.
- Ren is a very materialistic person; she spends her breaks on luxurious vacations and likes designer clothes and accessories. This suggests she comes from a wealthy background.
- There are several instances where Ren attempts to sexually harass Shouko.