It's literally that tutor's son, if not the sister's. The hair color and flashbacks gives it away. He must be mad and craving for revenge for his parents death.
OKAY WTF???? LEMME BEAT Y'ALL TF UPPP HOW DARE Y'ALL HURT THIS SWEET BABY. GET YOUR POOR ASS HANDS OFF MY BABY CAI. IMMA RIP YOUR UGLY ASS FACES. COME FIGHT ME HOES(ノಠ益ಠ)ノ彡┻━┻(ノ`Д´)ノ彡┻━┻┻┻︵ヽ(`Д´)ノ︵┻┻
It's literally that tutor's son, if not the sister's. The hair color and flashbacks gives it away. He must be mad and craving for revenge for his parents death.