Mc was male , i think he was in middle school or high school, kinda forgot.

He lives in church orphanage and one of the nun sister that take care of him and mc looks up to her as mother figure.

One day mc somehow got attacked by unknown person but got saved by a girl that revealed herself as vampire.

I think mc was from vampire family or something, and was like a heir to strong vampire bloodline. The assasin was fellow vampire that want kill mc because of power struggle beetwen vampire.

I also remember the sister that raised mc was famout vampire hunter and know mc was vampire. Both vampire organization and vampire was hunting mc.

This have like 4 volumes and fully translated in english. It was very old manga.

Hi
I looked it up a bit and this is the closest thing to what you described :

Cross x Regalia

Hope I helped 😉