Tsundere is a type of character who is cold and even hateful towards another person. But over time they start to show their warmer side as they begin to know the other person. They remain in "tsun" mode but become more and more lovey-dovey when in private with their loved ones. The word derives from the terms tsuntsun meaning "to be hateful to certain someone." While dere means "to become Lovey Dovey."