In Celtic mythology, a Kelpie is said to be a supernatural water horse that haunts rivers and lakes in Scotland and Ireland. Its mane is black, but its skin is said to be cold as death. It is said to lure mortals into water, specifically young children, into drowning so it can eat them. The kelpie tempts children to ride on its back, and once the victims fall for the trap, the kelpie's skin is said to become adhesive.
"Origin: England. They are foal-like water fairies. Also called water horses, they drag humans who ride them underwater to drown. They sometimes appear as men, but are easily distinguished by the seaweed in their hair. They make excellent mounts if they can be caught, but curse those who treat them badly. In some cases, their upper body is a horse and their lower body is a fish."
"Water sprites of Scottish folklore. Kelpies resemble horses and eat the grass that grows by the waterside. If you touch one, you will never be able to let go. Those who try to climb on a Kelpie's back are dragged underwater and drowned. Kelpies are swift of foot and, if caught, make excellent steeds. Treating them roughly, however, will result in a curse."
A group of Kelpies that resided in the Ueno region until Pellaidh forced them out. They act as a bridge for certain humans to cross the Kanda River near Ueno. They have a vendetta against Pellaidh for his previous actions alongside the humans and offer Flynn a deal in exchange for bringing them his head. After obtaining his head, the head Kelpie tosses it to his brethren to be eaten. Afterwards he offers to act as a bridge whenever the Samurai need one for helping them.
Hostile Kelpies appear in Shibuya and later in Midtown. They can teach Flynn the Diarama and Tarunda skills through their Demon Whisper. Kelpie may evolve into Valkyrie starting at level 42.
"A fairy of Celtic folklore that lives by the water. It looks like a horse. It drowns those who ride on it, but if you can tame it, it can be a valuable mount."
—Shin Megami Tensei IV Apocalypse compendium
Kelpie can be found within the Sky Tower. It can teach the Tarunda, Diarama and Trafuri skills through its Demon Whisper. Kelpie benefits from learning healing and support skills. Kelpie is also capable of transforming into Valkyrie at level 39.
"A horse-like fairy of Celtic folklore that lives by the water. It drowns those who ride on it, but is a valuable mount if you can tame it."
—Persona 5 background
Kelpie is the first Persona of the Strength Arcana and can be found as a Shadow in Kamoshida's Palace and the Aiyatsbus area of Mementos, with the title "Mad Marsh Horse." It is the only Persona to learn the Resist Brainwash skill and the first Persona to learn Sukukaja. When itemized through an Electric Chair execution in the Velvet Room, Kelpie will yield a Terror Claw skill card.