The monster of sadness(Crossover x male autistic reader)

This story isn't connected to my lore

You had a gf called Saki Yoshida. She was a kind and nice girl yet very shy. But her life went to hell. She became a drug addict and a prostitute and you tried to pull her away from this hellhole but she pushed you away and called you mean names. She soon died of an a blood loss after getting violated by her friends. You were there to see her die in your arms after she apologised to you. You snapped and killed everyone at sight. You became a monster driven by sadness and hopelessnes. After the massacre, you ran away as fast as you could from this shithole you called once home. Your life was never the same. You got adopted by an Granny called Seiko Ayase and you started dating her grandaughter Momo. And you were extremely protective of her. So much you almost killed a dog once cuz he almost bite her finger.