Ancient Japan is under attack by powerful beings called Kamikui, and it is up to the Oni and his band of eight beautiful female warriors to stop them. Each of these girls have unique skills, abilities, and personalities. They partner themselves with the Oni, Jin, to stop the miasma of darkness sweeping across Japan. Onigiri follows the escapades of Jin and his merry companions as they strengthen their bonds and fend off the demonic invasion.

Ren Mihashi was the ace of his middle school's baseball team, but due to his poor pitching, they could never win. Constant losses eventually lead to his teammates bullying him and reached the point where his teammates no longer tried to win, causing Mihashi to graduate with little self-esteem. As a result, Mihashi decides to go to a high school in a different prefecture where he has no intention of playing baseball. Unfortunately, upon his arrival at Nishiura High, he is dragged into joining their new team as the starting pitcher. Although unwilling at first, Mihashi realizes that this is a place where he will be accepted for who he is; with help from the catcher Takaya Abe, he starts to have more confidence in his own abilities. Abe, seeing the potential in Mihashi, makes it a goal to help him become a pitcher worthy of being called an ace.

Maiku Kamishiro's past has always been somewhat of a mystery to him. The only clue he has to who his family might be is an old photograph showing two young children, a boy and a girl, playing in a small pool outside of a blue house. In an attempt to find his family, he moves to this blue house and begins working as a programmer. He's living a comfortable life until the day two very different girls show up at his door, both in possession of the same photograph, and both claiming to be his twin. With no way to prove who is a relative and who is a stranger, Maiku allows both girls to move in with him until they know for sure. (Source: ANN)

Onyankopon watched over people long ago, but one day an old woman accidentally hit Onyankopon in the head with a mallet while mashing yams. Since then, Onyankopon has been nervous about greeting people directly, and so sends subordinates to speak to them and solve their problems. He will use Afrobeat and dance to help Japanese high school girls with problems such as dieting, love, and cramming for exams. (Source: ANN)