tsundere; hot-cold personality
Describes a character who is initially cold, aloof, or hostile but gradually reveals a warm, lovestruck side. Common in anime, manga, and otaku culture; now widely understood in Japanese pop culture.
She's a tsundere; she's usually cold but sometimes becomes incredibly sweet.
The heroine of that anime is a classic tsundere.
She's tsundere, so even though she seems cold at first, she becomes kind later.
Tsundere characters often appear in anime.