In the Naruto anime, Kagura Otsutsuki who was an alien "celestial being" could have children with Tenji and they had Hagomoro Otsutsuki. Normally 2 different species can't reproduce unless they have common ancestors. Were the humans and the Otsutsuki aliens related and had common ancestors before they met, was it an amazingly coincidence that they had practicaly they same genes or what? Humans can't reproduce with species who have 99% the same genes so they should have >99% identical to humans, is this ever explained why?
So...this is set in a world where someone who is adept enough can literally generate fire, water, electricity, earth and wind from their hands by weaving specific seals. I'm gonna have to ask that you just slightly suspend your disbelief on this one.
There's no explanation as to why this is possible, similar to how there's no explanation as to why whole eye transplants have such a high success rate among recipients of the Sharingan or coveted Byakugan (whereas in reality, that just isn't a thing).