Ninku(NINKU -忍空-Ninkū) is a Japanese manga series by Kōji Kiriyama. The original manga spanned 9-tankōbon volumes and was serialized in Shueisha's Weekly Shōnen Jump manga magazine between 1993 to 1995. A second manga titled Ninku Second Stage: Stories of Etonins(忍空 -SECOND STAGE 干支忍編-) ran from 1994 to 1995, but recently restarted in the seinen magazine Ultra Jump in October 2005, with its sixth tankōbon volume being issued in November 2008. It ranked number 21 among the top-selling manga volumes during the week of its release.