The caption says "Yukkuri Haafu" (Half-Yukkuri). I guess Yukkuri genome can interact with human sperm to breed humans with Yukkuri face features. We should not expect offspring of human females who had sex with Yukkuris, at least for now.
And then the half-breeds attract more humans, and THEY breed quarter-yukkuri, etc. until there are multitudes of mostly-human that all look like Touhou characters.