Topp is Oscar's foster father and mentor. He is aware how talented Oscar is as a Synergist, and feels that he is wasting his talents by working in the former's blacksmith.
Moorin is Oscar's foster mother. Someone he cherishes greatly.
Oscar's little brother. Ruth looked up to Oscar at first, but later treated him poorly because he believed that he wasn't a good Synergist.
Oscar's younger brother. Someone who he cherishes greatly, and the one who looks up to Oscar the most out of all his siblings. He hopes to be just like him one day.
Oscar's younger sister. Someone who he cherishes greatly.
Oscar's little sister. Someone who he cherishes greatly.
Oscar and Miledi have a complicated relationship. Although she regularly annoys him with her antics, he will follow her anywhere, even if she were to to go the depths of Hell itself. He also greatly cherishes her.
There is also an implied relationship of something more, but neither will admit it.
Oscar and Naiz get along rather well, spending hours talking and playing games, much to Miledi's annoyance.
He and Vandre can't see eye to eye on anything, constantly getting into verbal spats.
Ping hates Oscar due the constant attention that Topp Karg D. Orcus gives him, while under the impression that he is nothing more than a failure. He would bully Oscar every chance he got, as well and have him deal with his workload in addition to his own. While Oscar is not happy with Ping's treatment towards him, he does not try to fight back and does everything he can to placate the young noble. This, however, only serves to intensify Ping's hatred towards Oscar, which eventually leads to him kidnapping the orphans from Oscar's old orphanage.
Like the Liberators who learned of the Gods, Oscar was one of Ehit's archenemies from the faction. After his fellow Liberators were unable to start a revolution against Ehit due to instigating his worshippers to hunt down the Liberators, Oscar helped his fellow Liberators to create their own respective Great Labyrinths including his own Orcus Labyrinth with his Creation Magic as a means to pass down the Liberators' Ancient Magic required to slay Ehit and destroy his "game board" once and for all which ended up to success when Oscar's first Ancient Magic successor Hajime Nagumo slayed Ehit and his game of death is destroyed with him.
Although they have never met, Hajime learns the truth about the gods of Tortus through Oscar's message, which allows Hajime to realize the true danger of the predicament behind Ehit forcefully summoning him and his classmates to Tortus. Hajime holds immense respect for Oscar's genius skills as a legendary Synergist, as well as using Oscar's collection of historical documents, notes, alchemical tools and artifacts in his hidden lair to further advance his own Synergist skills.
Hajime takes in upon himself to fulfill Oscar's legacy with regards to creating the perfect maid golem.