Black-bellied little white rabbit✖️Innocent big bad wolf
First meeting: Can you be my brother?
Later: I want you to be my lover and husband, but I don't want you to be my brother.
Disclaimer: The male protagonist is not an LTP. He only started to have a romantic relationship with the female protagonist after she became an adult. Before that, he had always treated her as a younger sister.
Purpose: Facing life directly