NARUTO: Sasuke Retsuden - Uchiha no Matsuei to Tenkyuu no Hoshikuzu

Uchiha Sasuke heads for an astronomical observatory, far from the Land of Fire. There, he syncs up with Sakura, and together they dive into an undercover investigation in search of traces of the Sage of Six Paths! The two are soon drawn into a deadly conspiracy! The popular spin-off novel, now as a manga series! (Source: MangaPlus)