Kenta Usui

Kenta Usui is a student that transferred to Karin's high school. He is also her workmate. Kenta is the only human that knows of Karin's vampiric nature. He learned what she was after witnessing her biting three victims, one of which was his own mother. He has promised to keep this knowledge a secret. As his unhappiness causes Karin's blood to rapidly increase, she has taken it upon herself to cheer him up by making him a bento every day. He could not afford to buy his own lunch and is therefore grateful to her. (Source: Wikipedia)