So he really is Jin Sen's biological father, but why use the term 'biological father'? It is only used to distinguish when there are different father figures, suggesting that Jin Sen was brought up by someone else.
Considering that the legal restrictions on alchemists in Guboer are relatively looser, for some reason--- perhaps protection, perhaps something else--- this master alchemist named Hart had Jin Sen fostered elsewhere.
Qian Cangyi thought.
Upon confirming the other party's identity, he immediately assumed a more gentle demeanor. After all, the disparity in their statuses was too significant; Milo and Hart were people from entirely different worlds.
"I might add, this master alchemist also helped create 'The Only,' a game that has become a nationwide phenomenon, so… I'd advise you not to meddle in other people's family affairs," Elsa added.