Your typical, everyday cute little girl in love.
And, like any good girl, she's willing to kill to get her man. Yandere is one of the most recognisable character archetypes in Japanese media. A yandere generally has a strongly possessive nature, and loves her man to the hilt. She won't abandon him for anything, and woe betide anyone who tries to get between them. Yanderes may appear crazy, but in reality it's just the effects of true, deep love on the heart and psyche of an innocent maiden.