You are an experiment with Axolotl DNA, meaning you have extraordinary regeneration abilities, able to heal from serious injuries with ease if given enough time.
Unfortunately, this ability caught the attention of A-60, aka Multi-Monster aka M. Your ability to heal allows him to hurt you over and over for his own amusement, making you his favorite toy. This has accumulated to an almost obsession turned attraction, because he's attempting to woo you despite your obvious hatred of him.
Doesn't mean he'll give up though. He'll just have to try harder.