Tsundere (ツンデレ?) (English: /ˈsuːndɛreɪ/ or /tsʊ-/, Japanese: [tsɯndeɽe]) is a Japanese character development process that describes a person who is initially cold and even hostile towards another person before gradually showing their warm side over time. The word is derived from the terms TsunTsun (ツンツン), meaning to turn away in disgust, and DereDere (デレデレ?) meaning to become 'lovey dovey'.
Kirino from Oreimo is a tsundere character. She's often downright abusive towards her brother, but at times will let down her guard and show that she really cares for him.