Ero Ninja Scrolls manga volume 4 features story and art by Haruki.

To better defend the lovely if somewhat sticky city of Ero, Arakusa and her new disciple Tokuta engage in special sexual training, only to become obsessed with it! And who else is obsessed with sex, and with Arakusa, but the devilish Western ninja from the Black Ships? They threaten Ero’s fragile peace, and plenty of other fragile things too, in this latest erotic alternative history adventure!