Maksis was Maria's husband/lover. According to Jek, he wanted Maria because of her father's interest in folklore and the forbidden grimoire. Through deception, he took on a human form and grew close to the professor, and at some point he took Maria as his wife. Eventually, the two of them had a half-devil daughter, Ritsuka, who was the first child born with royal demon blood in 615 years. It is revealed in the game that he did care for Maria and their daughter to a certain degree.
Maksis is Ritsuka's father, and while the exact details of their relationship are unknown, Maksis was overjoyed at her birth. Though it was because of the grimoire's power, and not out of love for his daughter. It is later revealed in the game that he did in fact care about Ritsuka and her mother to some extent.
Roen is a loyal and faithful servant of Lord Maksis.
Mikukier, the head of the Arlond family, sealed Lord Maksis away.
Lord Nesta is an enemy of Lord Maksis.