When playing the the latest chapter and during the 1st conversation that Oscar and Asterion had, we were given a bunch of criterias that Oscar used to see weither Asterion was his father or not. The thing is i personnaly find that Lord Poseidon is the one most likely to be Oscar's father. For starters, Hermes did say that Poseidon descended to the mortal realm for the last 30 years trying to deal with his regrets the biggest being Asterion's torture and this duration lines up with Oscar's age being 21. Another thing is that Oscar's mother always refered to his father being a human and Greek gods have been known to pull this off. And the "Downed tapir" region have been described by Pedro to be almost empty of cell lines and towers that usually drove away magic and mythicals so Poseidon ending up there isn't too farfetched i mean their is a litteral skinless god chilling in the city. And Poseidon was described to have lost all sanity, even in the conversation he had with the Mc we couldn't guess who he was.
So what i think happened is that Poseidon descended 30 years ago, found his way to Downed Tapir, lost sanity and got completely into character and met Oscar's mom and then disappeared to meet the Mc 21 years later in the train station.
I don't think that their are that many possibilities for a "man" to be the father of a minotaure even in a place like Downed Tapir, but this is just a speculation.