A lesson without pain is meaningless, for you cannot gain something without sacrificing something else in return. But once you have overcome it and made it your own…

You will gain an irreplaceable full metal heart.

— 

Full metal alchemist.

so true.

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.