Souichirou, who is always referred to by his surname (as per Japanese standard), is the guardian of Lucia, who loves her as if he were her real father. Before Lucia was born, Nahashi was studying to become a mage, along with Lucia's mother Lilith and Lucia's father Lucif. He harbored an unrequited love for Lilith, but never got close with her as she was in love with Lucif.

(wikipedia)