Kanon is a female vampire, which is one of the strongest demonkin. She was helped by another demon when she was younger and so under his orders she attacks Youji. But after being defeated and well treated, she grows fond of him and their living, joining Youji and the rest on their adventure.

Humans are the Strongest Race
Elf? Dwarf? No! Humans are the strongest! I was summoned to a different world where humans are the strongest living beings. In my previous world I was just a normal everyday salaryman, but in this new world, I seem to have become a rare existence. I, who have obtained the strongest power through my race, have decided to enjoy this seemingly stress-free life to the fullest.