She is timid, insecure, and doesn't like to communicate with others. But it's the little sun next to someone close to you... The first heartbeat was because of that cold "promise".
He has a withdrawn personality and looks strong, but in fact he is lonely inside. The initial rescue was because he couldn't stand her cowardice in not resisting when being bullied.
In this world, no one is born for anyone, but if meeting her is fate, he is lucky. If she was lucky to meet him, she was grateful for her fate...