Ren Yamai is one of Shouko's classmates. She has an obssesive crush with Komi and secretly worships her even more so than Komi's classmates who admires her as a "class' goddess". When Hitohito, the male protagonist approached Yamai and asked her about Komi, Yamai jealously and violently threatens him.
In one arc, she kidnaps Hitohito since Yamai views him as a threat to her one-sided relationship with Komi. When Komi finds out about her villanous act, Komi retorts and "rejects" Yamai by saying that she gets to decide with whom she would be friends with which devasted Yamai.
Komi forgives her act and becomes at least an acquiantance to her. However Yamai continues to obsessively go after Komi going as far as orchestrating situations that would put Komi in a compromising situation. (usually to see Komi's underwear, grope her, or forced a situation of them just being together).