Saishuu Chikan Densha

In a crowded train, strangers are likely to end up being too close for comfort. But for some people, being too close is a comfort. When a poor conductor witnesses the bizarre yet inviting ritual of anonymous train sex, he jumps on the opportunity to turn it into a business. Every night after the midnight train ends its route, he turns it into a rolling bordello. Get ready to climb aboard... the sleazy train is coming.
(Source: Anime News Network)