Touhou Suimusou ~ Immaterial and Missing Power. (東方萃夢想 ～ Immaterial and Missing Power. lit. Gathering Dreams in the East ), commonly abbreviated as IaMP in English speaking circles, is a versus fighting game collaboratively developed by Twilight Frontier and Team Shanghai Alice released in 2004. It is numbered as the 7.5th installment in the Touhou Project because the events in the game take place place between Perfect Cherry Blossom (7th) and Imperishable Night (8th), although it was released after Imperishable Night.
IaMP is unique within the Touhou Project series in that it is a fighting game instead of the usual bullet hell. The game is also unique among fighting games for its heavy slant towards projectiles, tracing the series' shoot 'em up roots.
IaMP has a "graze" function, unique among the versus fighting genre, that allows the player to dash through projectiles unharmed provided the character has enough energy to do so. Not all projectiles can be grazed, however.
Spell cards, in this game, are special moves that have to be announced before they can be used. Each character can choose 1 out of 3 normal spell cards and 1 out of 3 overdrive spell cards to use before a match starts. The overdrive spell card replaces the normal spell card when the player's character has been defeated once. Also, when a spell card is announced, the player's HP replenishes for a certain amount.
In the story mode, there are spell cards that are available only to the enemy characters. A spell card can be "collected" when the player defeats the enemy character in a limited amount of time when the enemy's spell card is in effect, and that collected spell card would appear in a gallery in true Touhou fashion.
Spring has passed by the land of Gensokyo, a reclusive realm in the far east, and the cherry trees have since shed their blossoms. However, the hanami kept on going, with feasts being hosted day after day with no end in sight. Adding onto that, every time the feast is held, an unknown restless spiritual aura in Gensokyo also increases; however, nothing happens even while the spiritual aura rises, but when the spiritual aura rises, not a single person attempts to stop the feasts. As such, everyone who goes to the feast, be it human or yōkai, appear to be very suspicious.
Three days before the next feast, the heroines set out, each on their own, and attempt to investigate.
"I'll get to the bottom of this before the next feast!"
Eleven characters are available for play; all but one are returning characters from previous games.
- The miko of the Hakurei Shrine. She is troubled by the constant feasts in the shrine that she has to host, and goes to attack whoever she thinks is making her host all the feast.
- A magician. She acts as the secretary in charge of the feasts, though she has no idea why Gensokyo's having so many feasts.
- The maid of the Scarlet Devil Mansion. Sensing a mysterious qi in the feasts, she sets out to investigate.
- A witch who does not usually go out of her library. This time, however, she took responsibility in investigating the mist that has been blanketing Gensokyo.
- A half-ghost. Like Reimu, she goes slashing the suspects with her sword.
- A vampire who is thought to be one of the prime suspects in creating the strange mist, because she did it once before in Embodiment of Scarlet Devil.
- The ghost princess of the netherworld. She is another one of the prime suspects.
- A wandering yōkai who was never invited to the feasts but comes anyway.
- An Oni. Her powers allow her to collect the inhabitants of Gensokyo to hold feasts day after day, and scatter herself to become mist that covers all of Gensokyo.
- A Chinese-like yōkai that was included in one of the new patches of the game. She has no story mode.
On April 1, 2004, Twilight Frontier, famed makers of Eternal Fighter Zero, announced they would make a Touhou fighting game named Exciting Touhou 2. In its introduction page (now defunct), the group provided a trailer  and screenshots of that game, which appeared to be a version of WWE SmackDown! Here Comes The Pain with Touhou characters. (The WWE Smackdown! series is named Exciting Pro Wrestling in Japan.)
A day after the April Fool's Day, Twilight Frontier announced the production of IaMP with Team Shanghai Alice. Team Shanghai Alice was responsible for character design, the plot, stage design, system graphics, spellcard naming, and a portion of the soundtrack while Twilight Frontier took care of the rest.
The soundtrack of the game was compiled into an album named Gensōkyoku Bassui (幻想曲抜萃) which was sold on August 14, 2005. A significant portion of the soundtrack were remixes of existing Touhou songs.
- ZUN. Shanghai Alice Signpost. vol.5 2004/12/30 (Immaterial and Missing Power readme file)
- Immaterial and Missing Power: Official Site
- Immaterial and Missing Power introduction in Team Shanghai Alice's website
- Immaterial and Missing Power on TouhouWiki