Touhou Suimusou - Immaterial and Missing Power chronologically takes place between Perfect Cherry Blossom (TH07) and Imperishable Night (TH08). Henceforth it is referred to as TH07.5. Instead of being solely ZUN's work, Immaterial and Missing Power is a collaboration between ZUN and Tasogare Frontier.
While making preparations for the feast three days away, Reimu is distracted by a strange powerful mist that is covering Gensokyo. She and many other inhabitants of Gensokyo (such as Alice and Patchouli) go to investigate.
Touhou Hisouten - Scarlet Weather Rhapsody chronologically takes place about 1 year after Mountain of Faith (TH10). Henceforth it is referred to as TH10.5. Like its predecessor, Immaterial and Missing Power, Scarlet Weather Rhapsody is a fighting game, created by a collaboration between ZUN and Tasogare Frontier.
A bizarre phenomenon is occurring in Gensokyo. In the middle of summer, untimely rain and hail fall in the Forest of Magic, snow blankets Hakugyokurou, the Scarlet Devil Mansion is enveloped in a cloudy, dense haze, and the Hakurei Shrine is leveled by a sudden earthquake. Throughout the game, Reimu and the other protagonists set out to investigate the source of the strange occurrences.
Touhou Hisoutensoku - Unthinkable Natural Law is a standalone expansion pack to the fighting spinoff Scarlet Weather Rhapsody with five new characters. Combining this expansion with an installation of Scarlet Weather Rhapsody allows for the use of additional Touhou characters within the new expansion. Like its predecessors, Touhou Hisoutensoku is a collaboration between ZUN and Tasogare Frontier.
A mysterious giant is seen wandering around Gensokyo. It can suddenly appear and can just as suddenly vanish seemingly without a trace. Everyone who sees it becomes curious and wonders about the truth behind this strange sight. Sanae, Cirno, and Meiling each have their own fears and dreams about the giant, and each sets out in pursuit of this roaming behemoth.
In the wake of so many incidents beyond their control, the Human Village as fallen into disorder and nihilism. Believing that religion can restore order, some of Gensokyo's most prominent adherents of Buddhism, Taoism and Shinto all want to take this chance to expand their particular faith's influence.