Yandere

    Yandere is a Japanese term for a person who is initially very loving and gentle before their devotion becomes destructive in nature, often through violence. The term is derived from the words yan (ヤン) meaning a mental or emotional illness and dere dere (デレデレ) meaning to show affection. Yandere characters are mentally unstable, often using extreme violence as an outlet for their emotions.

    Source: Wikipedia