Responses
I don’t think something being very obviously purposely omitted counts as a “plot hole”. The author is very very clearly trying to keep it vague, and to me it seems in order to emphasize that it doesn’t matter, they are his dads. Does it actually matter? Irl it’s complicated with adoptees and their birth parents so it’s def not as straightforward but this manga absolutely feels intentional in omitting it

It's so cute I'm gonna ignore a baby just appeared out for nowhere.
... no I'm not. It's so cute but the plot holes O.O wasn't seme from a good family? I guess they could have disown him for dropping out of collage. The baby? Is it his sister's or some relative's? There was a mention of relation by blood, but he said it's not his. We have not heard or seen any siblings, so whose baby is it?? If it was a sibling, why didn't the baby's grandparents help? I hope there is a sequel, that gives more info