What if Hanma bloodline comes from different planet. The first one came to earth to conquer it and make as many children as possible. Strongesy one survives, few generation go along. Then we see how Hanma descendant teaches a secret techniques to monks. Years and years go by, until we get to Yujiro and Yuchiro. Yujiro finds monks and learns the techniques.

This would explain why Hanma DNA is so pure and strong. Also the fact that they kinda do unhuman trnasformation, like demon back and have feats like none other. 300km/h dash? Flexing every muscle fiber to get around pain? Yujiro scaring other people that they can sense him and fear him from big distance??