Fafner is immoral and inhuman. He doesn't care does human suffer to get his goals, but is an evil genius (because of this, he protects the Chamber of Wisdom).
Fafner was designated by Andreas to arrange an ideal human being to create the new Odin's Saphires with his life. He probably knows about Loki, because according to Mu, he discovered that something is growing inside Yggrasil, and Fafner doesn't get surprised. He has various hospitals (probably, each one in each village, because every village must be a hospital to his people's) where he tests humans of the nearest village.
Fafner arrests the villagers of various villages of Asgard, searching for the perfect human to his experience, and Mu goes to investigate the disappearance of citizens of a little boy's village; Mu allows Fafner captures him, to inside the Yggdrasil, discovers its secret. After Fafner tries test Mu, Mu stop his pretending and fights against Fafner, and Aiolia and Lydia arrive there. The place is destroyed and Fafner goes to another hospital, where he finds Helena, and discovers she is a perfect human to create a Sapphire, and even creating one, Aphrodite stops his experience and Andreas destroys the place.
How Helena dead, Fafner secretly catches her brothers because they must be the same compatibility, so, can be used to create new sapphires. He created 6 sapphires and after, Andreas uses them to control the mind of his God Warriors.
Fafner keeps the brothers of Helena in the amethysts to blackmailthe saints, and where Mu arrives in Chamber of Wisdom, Fafner is easily defeated but hits Mu with his new power; Deathmask arrives and asks Mu to go to Andreas's room, because he wants to avenge on Fafner, because he was the guilty killing Helena. Fafner is sent to Yomotsu Hirasaka, and Deathmask goes there too, but there, they see the brothers of Helena walking for the death hole, and if Fafner dies, they will die too. So, Deathmask just buries Fafner in the floor to be trampled in his face until he dies.