We're going to Refresh!
Story starts with the couple emerging from their nest after winter, but they are unable to find food as the true spring hasn't arrived yet, and are forced back into their nest by the arrival of cold wind. There, they complain about the lack of food, and recall the promise to make little ones once spring arrived.
Then Marisa suggests that they just do so, believing that food will come soon. It starts off normally, then suddenly Marisa feels the urge to pee, and despite Reimu's objections, does so inside Reimu's mamu-mamu. After a small argument about the smell, Marisa tries to pull out, but can't.
This is because the pee has melted their penipeni and mamumamu, which then rejoined. They could have separated if they pulled harder, and still retain reproductive capabilities, but because of the pain involved, they don't. Because of that, these two are unable to move, and will get chilled to death in their nest.
Illustration: post #16308