Touhou Gouyoku Ibun: Sunken Fossil World

Black water gushed out onto the surface. The water released an odd odour, and was hard to get off once stuck to one's body. It was not something that you could use as your everyday water.
Some saw the gushing water as misfortune, some as good fortune; some saw it as holy, while others as evil; some saw it as a natural disaster, some saw it as a business opportunity, various theories were tossed around. Some even started a festival and made a fuss.
But not long after, an event occurred that put a horrific damper on their buoyant moods. From the springs that they drank from, the beautiful clear streams, the hot springs at rest spots... from every location it possibly could, the black water began to gush out.

Touhou Gouyoku Ibun: Sunken Fossil World is the 17.5th installment of the Touhou Project, created by Team Shanghai Alice, with Twilight Frontier's collaboration. The game is described as a "horizontal side-scrolling danmaku water action game" on the official website.