He's from Okinawa so i guess that's part of it (basically the JP equivalent of being in the south?) so i'm sure his skin would've ended up tan anyways from being out in their sun or so
I think his hair is a lil darker as a baby, but it is intrresting, I looked it up and I hear folks from Okinawa and a couple other islands of Japan are a little darker in skin color than folks from the more northerly regions. Not African or South Asian dark, of course, but enough to be noticeable. It might be a little exaggerated for our hero but I wonder if hes from Okinawa or thereabouts.