Reminds me of Sorena's only grandchild passing herself off as a boy known as "Albus", even though her true gender was revealed, she is still called by that masculine name even in the five-year spinoff of Grimoire of Zero.
But Dororo here, really did not need to hide her gender like "Albus" did to make people think that the renowned Mooncaller Witch had no descendants.
Plus, Haykkimaru makes me think of Toph Beifong who is still a master earthbender and, later on, metalbender in spite of her blindness, being freely capable of "seeing" her surroundings and people with her bare feet as well as discern truth and lies from another in place of ascertaining one's true nature by detecting the color of their inner essence/soul/spirit.
His spirit/mind/vital essence still living within a counterfeit humanoid body, just like Kikyo and then the spirit of the centuries-old reindeer or deer-demon girl Rion, eighteen years after Kikyo had died for a third and last time.