Yachiru's Friend! The Shinigami of Justice Appears!

While Kenpachi vents his energy by toppling trees in a forest outside the Seireitei, Yachiru wanders off and senses a familiar Reiatsu. Nearby, a young woman named Mayu is saved from a Hollow by a cloaked Shinigami who introduces himself as Masayoshi. Yachiru joyfully leaps into his arms, calling him Mappy, and the three settle at his riverside camp to catch up. Masayoshi says his work suits him because it lets him roam in search of the Hollow that murdered his wife, and he vows to destroy every Hollow in existence, oddly declining the sweets Yachiru offers.

As Mayu grows visibly fond of Masayoshi, Yachiru begins noticing that things do not add up: he cannot recall his wife's name, and he claims to dislike the sweets he once loved. When Mayu is later seized by a vengeful Hollow and a swarm surrounds them, Masayoshi cuts them all down, but his eyes flash black with red irises. Confronting him afterward, Yachiru reveals that he himself is a Hollow, possessed years ago and driven to kill his own wife, the shock of which reverted him to Shinigami form even as the Hollow slowly consumed him, erasing her name and his taste for sweets.

The distress of accepting the truth lets the Hollow partly surface, frightening Mayu, and when the original Hollow lunges for her, Masayoshi throws himself between them, shattering its mask while taking a mortal wound. Collapsing, he apologizes to Mayu for failing his vow, and she weeps as he thanks her. Yachiru offers him one last sweet of his favorite flavor, which he savors before dying. A subdued Yachiru returns to Kenpachi, who tosses her a bag of candy and draws a small smile.

Yachiru reunites with her old friend Masayoshi, a Shinigami hunting the Hollow that killed his wife. She uncovers that Masayoshi is himself the Hollow, having unknowingly killed his own wife while possessed before reverting to Shinigami form. Masayoshi sacrifices himself to shield Mayu from the vengeful Hollow, breaking its mask, and dies after enjoying a final sweet from Yachiru.

An anime-original episode with no manga source, this is a self-contained side story centered on Yachiru and Kenpachi outside the main plot. Its Shinigami Illustrated Picture Book closer shows Yachiru gathering a meal in Rukongai only to admit, along with Kenpachi, that the pair are lost on their way to Seireitei.