Taimanin Asagi is a visual novel first released in Japan by Lilith Soft in 2005. Earlier this year listings for it showed up on Steam—announcing a free first episode to be followed by three paid episodes—which have since been removed.
Taimanin Asagi would certainly have been a controversial game for Steam to release uncensored. It's about sexy ninja who hunt demons, then are captured, tortured, and repeatedly violated in detail. And while games with boundary-pushing adult content like Saya no Uta have shown up on Steam this year, they've done so with their more explicit elements removed (in the case of Saya no Uta the cut content is available via a patch, but one that has to be purchased from a separate website). Taimanin Asagi on the other hand showed every sign of being released uncut, with explicit imagery right there in the Steam page's screenshot section.
Fans have picked up on a tweet by a Lilith employee which mentions, in translation, that "Steam is very strict in judging visuals that may be suspected to be minors" as evidence that Taimanin Asagi was removed from the storefront because of a character wearing a schoolgirl outfit. But maybe not. Steam's approach to adult content can often be baffling.