Thanks for the link!
I've never actually seen an East Asian ADULT with such aggressively natural blond hair as Yuudai, not even in pictures, though I've seen quite a few East and Southeast Asian kids with light brown hair like in your link that disappears when they get older
I also know about certain populations in northern South Asia and Central Asia (including Far West China) that have lighter pigmentation, especially up in the mountains. Some of the Hmong having such color is a surprise, though.
You ever heard of some naturally blond populations among the very melanin-rich Melanesians? I thought it was because they were seafarers, and their hair just got sunbleached, but no, that Beyonce blond hair is genetic! Super weird.
But back to the topic at hand!
I have nothing more to add. Except this drawing of Yuudai's father.