His charisma obviously came from being a clone of Klaxxo-hime and having natural dominion over anybody with yellow-blood-cells.
It's why he got along with Zero Two so well. Everyone falls in love with him. People are heartbroken when he forgets about him. He's more important to his fellows than Papa. They lose faith in GOD over him.
Zero Two was obviously not a clone of Hime, but some kind of Klaxxo-mutant. She's not Blue. You don't just become another species because you drink some shit. Hiro was a Klaxxo from birth, hence his amazing potential. Maybe all of Squad 13 was meant to be at some point, a Klaxxo-hybrid.
But they abandoned this idea.