アニメ character that went insane from someone dying? mine is mai :3 (from mai hime)

Poor Thief King Bakura had to watch everyone in his village sacrificed when he was young :(

shoin sonozaki went insane after the person she loved dissapered and never came back
she killed all her フレンズ her sister grandmother and another dude who i forgot

Koga

a アニメ character that went insane from someone dying would be Doom from Deltora quest after his wife was killed he try to go to the shadow lands to kill who did it. but he failed

Not the best example but all I could think of.Ed Elric. He tried to bring his mom back to life after she died. He's a little crazy. XD

Light from Death Note. After he killed L, he laughed evilly on his grave