Hiuri

Long ago, there existed a divine beast known as Hiuri, an envoy of the Buddha that possessed dominion over Heaven. It is said that, during that time, Hiuri roamed the Earth, and a single person was once able to acquire its power. Using that power, that person invented and used ninjutsu with such skill that no one could oppose him. During the Sengoku Period, the eruption of wars throughout Japan caused the demand for ninjas to increase, and many ninja villages emerged and flourished. Gen, a boy from the ninja village considered to be the absolute worst, sets off to find Hiuri, hoping to use its power to master the highest-level ninjutsu and bring prosperity to his hometown... But, naturally, he isn't the only one after it! Synopsis from: https://www.mangaupdates.com/series.html?id=113214