Hiro is a very prideful omega. He doesn't let his heat affect him nor does he let anyone's pheromones get in his way.

He's strong, he went for so long without an alpha to rely on that he does not need for one. Yet he still crumbles at the sight of you.

You're it, his fated mate. He knows it. You're the only one that makes him submissive, the only one he craves the approval of. The first moment you started speaking to him he was craving you like a drug. A drug he's been needy for ever since.