In the manga, Natsuhiko is the eldest sibling of the Miroku Seven in the Arms of the Goddess arc. He occupies the same body as seven other entities (his siblings) and hates Midou Ban. In the anime, there are only two bodies that inhabit the Miroku body: Natsuhiko and Yukihiko.
He is the "leader" and very seldom will the other siblings defy him. He especially likes to push around Yukihiko, the youngest Miroku. He is a very controlling person, and also the very cunning.
As stated, in the manga there are 7 bodies inhabiting Miroku's body. From oldest to youngest, they are Natsuhiko, Hikage, Ukyou, Tsubaki, Tokisada, Kirara, and Yukihiko. They are not multiple personalities, they are literally 7 souls in 1. They switch to a different person in situations that best suit the Miroku fir for the job. If one of them gets hurt they can switch out and the damage from the previous Miroku is erased.
Natsuhiko's weapon is a katana. He's extremely strong, he's in Akabane and Ban's league. He is the one who blames Ban for killing Eris. Natsuhiko's blade attack is called Immaterial New Moon, which creates something out of nothing.
Ukyou's weapon is a sickle. His sickle is made of metal but for some reason didn't conduct Ginji's electricity. He is very acrobatic.
Tsubaki's weapon is twin daggers. His specialty is close range and he seems to swear quiet a bit.
Tokisada's weapon is a long heavy katana. He is hot headed and usually charges head on into a battle. He has a scar on his left eye.
Kirara's weapon is a spear. She's extremely fast but lacks strength. She's the only girl in the family. When she fought Ginji, he thought she was really a guy. Probably since the rest the Miroku's are guys. Well, Ginji and Kirara were fighting, Ginji said he wasn't gonna hold back anymore cause he knows she's a guy now. But he was wrong, he lifted up her shirt and saw her boobs. Ginji is surprised that the body can change to female.
Yukihiko's weapon is a small bladed disc that weighs about 200lbs. The blade spins extremely fast and creates a huge gravitational pull. His attack is called Material Full Moon, and turns everything into nothingness. Yukihiko is the strongest Miroku. Ban says so during his fight with Akabane. Ban sensed Yukihiko's presence for a bit and said it felt like air.
The Miroku's hate Ban because they think he killed their eldest sister Eris.