Sam Gladiator is the yandere for Sookie in Yandere High School.
Background
Sam grew up with his (possibly) single father in Japan. He didn't have that many friends until his father set him up with a kid named Taurtis. When he entered high school, he tended up developing feelings for her.
Yandere Traits
Sam is obsessed with Sookie up to the point where he attacks his friend, thinking that he may be a rival for Sookie's love. After she confessed she's a lesbian and is involved with SoulOwl, Sam decides to keep pursuing her. At one point, he attempted to poison Soul, but Sookie ended up poisoned instead. He even dressed up as a girl in hopes that he would win her affections that way.