Sexy Timetrip Ninjas is the 27th film in the incredibly un-PC Groper Train series, the Japanese male-fantasy-fulfilment Pinku phenomenon in which pretty passengers on packed trains are only too happy to be sexually molested in public by total strangers. This one begins in early-Edo period Japan, with Lord Sanada entrusting ninja Sarutobi Sasuke (Yukijirô Hotaru) with a scroll which, when decoded, will lead to the hidden treasure needed to ensure the clan's continuing supremacy. Shortly into his mission, Sasuke is attacked by sexy female ninja Kagero, who has been ordered by Hattori Hanzō to try and steal the scroll.
Obviously, a 17th century period setting offers zero opportunity for tawdry train-based titillation, so the silly plot sees an earthquake throwing the two warring ninjas into a time-warp, the pair arriving in Tokyo circa 1984 where a surprised Sasuke suddenly finds himself on a packed train and the groping begins, the ninja immediately sticking his hands down the panties of the nearest cutie for a good fondle.
From herein on in, the film proves to be little more than an excuse for a series of racy sex scenes, with an absolute minimum of plot progression to drive the steamy action: Kagero hides from Sasuke in a Shinjuku brothel where she subsequently finds employment, using her ninja skills to offer a unique sexual experience to her clientèle; Sasuke hooks up with Tsuta, the girl he groped on the train, who coincidentally turns out to be an ancestor of Hattori Hanzō; and talent scout and vibrator-wielding 'groper train' pervert Kirigakure (Yutaka Ikejima)-'who dispenses battery-operated pleasure to women before offering to make them famous-'turns Tsuta and Kagero into a sexy ninja pop duo.
Eventually, after lots of over and under the gusset frottage and plenty of not-too-explicit nookie, both Tsuta and Kagero help Sasuke decode the scroll, collect the treasure, and travel back to the 17th century to indulge in further sexy shenanigans. Although the plot might be weak, the 'groper train' material awkwardly shoe-horned into proceedings, and the ninja action almost non-existent, there is no denying the film's powerful erotic charge and its general sense of fun, for which I rate it a very reasonable 710.
Review by BA_Harrison from the Internet Movie Database.