Maria was Maksis's human lover and the mother of his daughter, Ritsuka. Maksis got close to Professor Tachibana so that he would allow him to marry Maria. Eventually, Maksis was granted his wish, and he and Maria married. However, for all of his ambition, Maksis did love Maria just as she had loved him.
Ritsuka is Maksis's daughter which he had with Maria. Maksis was overjoyed at her birth for both the Grimoire and herself. Maksis truly loved his daughter, even sending his loyal servant Roen to watch over her, which Roen misinterpreted to mean that he wanted the Grimoire within her.
Roen is Maksis's most loyal servant, and serves him faithfully with all of his being. It is unknown if Maksis appreciates Roen's loyalty and efforts to bring him back. However, he did send him to watch over his beloved daughter, Ritsuka. Roen, however, misinterpreted this to mean that Maksis wanted the Grimoire within her so that he could return to power.
Mikukier is the one who defeated Maksis and sealed him away. Afterwards, Mikukier took his place as the demon king.