Momo is a pink, squirrel-like Onryo with a cream-colored face, limbs, and a flame-shaped tail that wags when cheerful. Originally a cheese-obsessed flying squirrel, his tragic demise in a mouse trap—triggered by a case of mistaken rodent identity—transformed him into a vengeful spirit. Seeking redemption, he honed his flying skills, indulged in endless meals, and embraced a plumper, more endearing form.

Rescued by the YSP Club from a cheese-baited trap in Sword Tower, Momo repays their kindness as a loyal ally, ferrying multiple riders through the skies by enlarging his body. His energetic catchphrases, "Desu-nee" and "Momo dayo!", mark his spirited entrances.

In *Yo-kai Watch: Wibble Wobble*, Momo aids players during limited-time events with defensive boosts and damage nullification. His upgraded Y-Kakusei Momo form, introduced later, amplifies damage and defense in challenge gates. Both variants wield the "Momo Glider" Soultimate Move to bolster attack power, with Y-Kakusei Momo randomly inflating Wib Wobs.

A mischievous prankster, Momo once left droppings resembling strawberry chocolates, nearly tricking a character into eating them. His name nods to "momonga" (dwarf flying squirrel) and the Japanese term for pink or peach. Despite his squirrel roots, his rotund frame and cheese fixation earned him the tongue-in-cheek moniker "Fat Rat," playfully evoking the aesthetic of a classic Dragon Quest foe.