A shape-changing creature, his name (roughly, &quot;sonic ball&quot;) is fairly descriptive. He is usually depicted as a round, yellow sphere with a face, variably with wings or arms, deep voice, and a loud temperament. Often, when getting emotional, he will transform into an extremely muscular full human body. In spite of being such a bizarre creature, he is for some reason the leader of Shinobu&#039;s ninja clan. Onsokumaru is perverted, lecherous, messy, loud, a cheat, and greedy. He imagines softcore-pornographic fantasies about Shinobu and Kaede, either for his own personal pleasure or to enthrall or persuade the male ninjas into helping him. On the other hand, he is often friendly, and has a silly playful side. (wikipedia)

Kaede is a normal school girl who was studying for her exams for school when suddenly she is interrupted by Shinobu, a girl who is a ninja-in-training, attempting to complete her exam. The problem is, in order for her to successfully complete her exam, she must steal one of Kaede's panties! 
In Kaede's attempt to stop Shinobu from stealing her panties, an unexpected friendship is forged between the two. Kaede soon becomes engrossed in Shinobu's world, surrounded by partying ninjas and a yellow pac-man like thing by the name of Onsokumaru, who claims to be the master of all ninjas! 
[Written by MAL Rewrite]

[Wiki (jp)](https://ja.wikipedia.org/wiki/若本規夫)

Used to work for the Tokyo Metropolitan Police Department Riot Police.

Shinobu is the only girl that goes to the secret Ninja Academy, which is presided over by a strange, yellow, ball-organism, Onsokumaru. While he knows nothing about being a ninja master, he loses no opportunity to exploit the dim but cute Shinobu. On a mission to steal all the panties from area high school girls, Shinobu meets Kaede who gets drawn into the surreal, ecchi, but fun world of Shinobu.
 
(Source: Anime News Network)

The innoncent ninja Shinobu, super-handsome-boy Otonomaru, and their merry band of friends are back! 
The official sequel to the legendary gag manga "Ninin ga Shinobu Den" makes an unexpected return in the Reiwa Era! 
Enjoy the dazzling world of Ryoichi Koga! 
 
(Source: Comic Newtype, translated)