Shuumatsu (Weekend) features a heavy rebalancing of the rates for dropped items and Satori's Learning, changes some of the recipes (with the most notable one being the recipe for the Kusanagi, which now only requires 5 Iron as opposed to 30), removes the feature that made you lose all of your "unsaved" items after getting wiped out in a dungeon, and adds a few new things such as a mini-map and an easy mode you can toggle on or off whenever you want. On easy mode, you deal more damage, take less damage, your status effects have a higher chance to work and the experience penalty on killing enemies at a lower level is reduced. You can also now refight the final boss whenever you want during the expansion, which means that Kagami's Hyper Fang Crush is no longer permanently missable and can be learned by Satori whenever you want.

It's a normal day in Gensokyo when Reimu Hakurei notices a strange fog rolling in. All across Gensokyo, residents witness this fog weakening and killing a great many lesser youkai. At the behest of Yukari Yakumo, she joins forces with Marisa Kirisame, Sanae Kochiya, and Aya Shameimaru to investigate the fog's appearance...