Yume 2kki - Menu Theme 87 [Read Desc]

Obtained in an isolated section of Quarter Flats accessible from the Somber Waterfront.
In order to access the Somber Establishment's convenience store, you need to visit Sepia Clouds World at least once. The Crimson Night has a chance to activate every time you leave the store, but it shouldn't be too hard to get.
As demonstrated, you need to visit the Weird Room in Fish Person Shoal's deeper shoal to access the theme.
The quick detour in Somber Waterfront was an attempt to unlock the Loquat Orchard connection, but I'm not sure if I did it correctly.