"One of the four oni Chikata Fujiwara was said to have controlled during the Heian period of Japan. He could control the winds and blow all his enemies away."
—Shin Megami Tensei III: Nocturne compendium
Fuu-Ki is one of the four Oni that were part of the Mantra demons' elite force. But they made a mistake which angered Thor and they were forever banished from Ikebukuro. The once elite Oni group became mere petty thieves who mugged anyone going through their scattered hideouts around the Ikebukuro Tunnel.
Fuu-Ki's hideout is located in the out-of-the-way tunnel within the station close to Asakusa, riddled with trapped surfaces. If the Demi-fiend approaches him, Fuu-Ki will laud the former for going out of his way to get here, and will offer him a good time with some women in exchange for money (he's lying, of course and will pocket the money without doing anything). If the Demi-fiend refuses, Fuu-Ki will be angry and a fight will ensue. Throughout the encounter, Fuu-Ki will mention killing him as a big mistake, and considers himself "too important" to die for some reason.
Shin Megami Tensei IMAGINE
Fuu-Ki can only be obtained through fusion. He appears as a field boss on Shinjuku field when summoned by one of the charms the Yaksini NPC in Ichigaya Camp's B11 will trade for magnetite.
Shin Megami Tensei: Strange Journey
"One of the four oni controlled by Fujiwara no Chikata, it sends hurricanes to blow away its enemies. Some say that Fuu-ki is the original ninja."
—Shin Megami Tensei: Strange Journey Compendium
Shin Megami Tensei IV
Fuu-ki controls a Domain over a relic in Ikebukuro Station - East Entrance. Defeating him earns the relic Small Fridge, which is required for the Challenge QuestRelic Recovery: Small Fridge.
Fuu-ki is one of the demons to first attack Walter and a Casualry when they arrive in Tokyo. The Black Samurai arrives and defeats the demon before it can harm them.
Shin Megami Tensei IV Apocalypse
Fuu-Ki can teach Nanashi the Zandyne, Fog Breath and Dark Sword skills through his Demon Whisper. He benefits from learning Force, Physical and support skills.
"One of the four oni controlled by Fujiwara no Chikata, it sends hurricanes to blow away its enemies. Some say that Fuu-Ki is the original ninja."
—Persona 5 compendium
Fuu-Ki appears as a mini-boss in Kaneshiro's Palace. When the Phantom Thieves use the communicator to separate the guards, the Shadow that reports to the monitor room will transform into Fuu-Ki when confronted. Fuu-ki also appears alongside Sui-Ki and Kin-Ki as another mini-boss encounter.
Yuya Uchimura's Shadow will also take the form of Fuu-Ki when confronted in Mementos during the quest "Ending the Boyfriend's Abuse." Shadow Uchimura resists Physical attacks and Gun attacks, and does not have a weakness to Electric skills. He will also use the Swift Strike skill to attack after attempting to buff with Tarukaja.