Yandere (ヤンデレ, Yandere?) is a Japanese term for a personality that is initially loving (spoony) and then combative (cranky), often brutally so. Yandere is a combination of the two words yanderu (病んでる, yanderu?), meaning to be sick, and deredere (デレデレ, deredere?), which is defined as exhausted or lovestruck. Yandere is the antonym of tsundere were a person is initially cranky and then later turns spoony.
Usually these girls are first presented as timid, shy and weak in varrying degrees, which are more or less traits that stereotypically describe young Japanese girls. Additionally, these yandere girls have darker aspects of their personality that, as noted above, often goes beyond simply being cold[3] and can turn very violent, even leading to the girl committing murder. This dark side is most of the time kept to herself and is heavily influenced by the individual's past, which usually amounts to being emotionally stressful for the girl in question. Also, the yanderekko will often be paired with the male main character of the series she is in and due to events involving him in the plot, will cause her to turn violent and psychotic.