Velten is a demon and has been friends with Vivi since they were kids. He cheers up Hana whenever Vivi gets mad at her. He has convinced Vivi that touching Hana won't kill her (in the same way that a flower wilts at a demon's touch).
He has a fiancee named Ellinor whom he refuses to marry due to fear of commitment, and a fondness for all females.(Also because of a fear that he would taint her.) Since Velten is the reason Vivi is willing to touch Hana, Hana is willing to act as his girlfriend when he wanted to chase Ellinor away by turning her into Nigou (an older version of herself) with the use of a potion.
After Ellinor finds out the truth, she moves in with Velten, though they stay unmarried. Velten is a baron, being demoted from Count for flirting with daughters of the Elders. He is very cheerful and it annoys Vivi because of that.
He is the only one of the demons who has no problem with the sun. The others and especially Vivi think it's too bright.