Yuno Gasai

Yuno Gasai is one of the two main protagonists (and the most iconic character) from the anime/manga Future Diary (Mirai Nikki).

She is a beautiful, pink-haired high-school girl who appears sweet, polite, and deeply caring on the surface — especially toward Yukiteru "Yuki" Amano, the male lead, whom she obsessively loves. However, Yuno is actually an extremely unstable, violent, and psychopathic yandere.

Key traits:

• Extremely intelligent and strategic
• Ruthlessly manipulative when necessary
• Possesses exceptional combat skills and cunning
• Completely ruthless toward anyone she sees as a threat to her relationship with Yuki
• Willing to kill, torture, or betray almost anyone (including friends, family, and innocent people) without hesitation
• Her obsessive love for Yuki drives nearly all of her actions

Her catchphrase and behavior have made her one of the most famous examples of the "yandere" archetype in anime.

In short: Yuno Gasai = sweet pink-haired girlfriend on the outside + terrifyingly murderous stalker on the inside.