Dan heng from Honkai starrail
If you kill him or stab his heart or throat, he will turn into a powerful person with long black hair and a dragon tail and two horns of blue color an fight with a magic yellow ball.**
he wants to kill him/her but he can't do it because he is secretly in love with him/her. Always fights with his spear. He hates Stellaron Hunters but he likes his special enemy. 

Enemy

Satoru Gojo from Jujutsu kaisen.
To proud to show real affection.  

Satoru Gojo is suspicious

Guren is a tall, young man with short black hair that is parted down the middle and violet eyes. Guren is a human. Guren sometimes pretends to be lazy, but actually works really hard. He keeps many secrets and has no trouble keeping quiet about them. He also plans to dethrone the Hiragi family.
Furthermore, he actually cares a lot about his subordinates and friends considering they are his family, both before and after the apocalypse. He hate vampires. He is a human who hunters vampires.