Sui-Ki (水鬼) whose name means "Water Oni" is of the four oni controlled by Fujiwara-no-Chikata (藤原千方) during the mid-Heian period. Sui-ki can freeze anything to the core.
"One of the four oni Chikata Fujiwara was said to have controlled during the Heian period of Japan. He could cause floods with the swing of his arms."
—Shin Megami Tensei III: Nocturne compendium
Sui-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.
Sui-Ki's hideout is located around a trapped area within the tunnel after going through a pitfall. He presents himself as a cold demon who would leave those who demonstrate courage alone. If the Demi-fiend feigns cowardice, Sui-Ki will attack.
Upon defeat, Sui-Ki expresses curiosity towards the Demi-fiend in his last few breaths, openly wondering if he's a demon or a human.
Shin Megami Tensei IMAGINE[]
Sui-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 can cause floods at any time. In the Taiheiki, Ki no Tomoo succeeded in expelling the oni by reading a Japanese poem."
—Shin Megami Tensei: Strange Journey compendium
Shin Megami Tensei IV[]
Sui-ki has placed a Domain over a relic on Shinjuku's East Entrance Main Street. Defeating him obtains the Corked Bottle relic needed for the optional main quest Bring Back Wine.
Sui-ki are later encountered as normal enemies in Infernal Tokyo.
Shin Megami Tensei IV Apocalypse[]
Sui-Ki can teach Nanashi the Bufudyne, Rakukaja and Mabufudyne skills through his Demon Whisper. He benefits from learning Ice, Physical and support skills.
Shin Megami Tensei V[]
"One of the four oni controlled by Fujiwara no Chikata, it can cause floods with the swing of its arms. In the Taiheiki, a brave courtier named Ki no Tomo-o expelled the oni by sending them an elegantly phrased threat in poetic form."
—Shin Megami Tensei V lore
Persona 5[]
"One of the four oni controlled by Fujiwara no Chikata, it can cause floods with the swing of its arms. In the Taiheiki, Ki no Tomoo expelled the oni by reading a Japanese poem."
—Persona 5 background
Sui-Ki is the fourth Persona of the Moon Arcana and can be found as a Shadow in the Kaitul area of Mementos, with the title "Floodbringer Demon". He is one of three Personas to learn Headbutt and the first Persona usable in battle by the protagonist to learn the Bufula skill. He is the only source of the Null Nuke skill and the first Persona to learn Mabufula. When itemized using Electric Chair execution in the Velvet Room, Sui-Ki yields a Mabufuskill card.
Sui-Ki first appears in Kaneshiro's Palace as a Shadow that acts as an enforcer for Shadow Kaneshiro. They will first appear alongside two Oni during the Phantom Thieves' initial escape from the area. They will later be encountered again as one of the guards in the Banker Passageway, holding a key that the party needs to proceed deeper into the palace.
Sui-Ki's Shadow title is now "Raging Water Demon." When itemized through Electric Chair execution, Sui-Ki will yield a Bufula Skill Card. During a fusion alarm, Sui-Ki will yield a Mabufula Skill Card.
Persona 5 Tactica[]
"One of the four oni controlled by Fujiwara no Chikata, it can cause floods with the swing of its arms. In the Taiheiki, Ki no Tomoo expelled the oni by reading a Japanese poem."