Mana Walker is Allen's foster father, having taken him in after Allen was abandoned by his biological parents because of his deformed left hand—a result of his Innocence. The two formed an incredibly close bond over time, and Mana essentially became Allen's true father figure.
Mana's death remains somewhat unclear, though the anime depicts an overturned carriage at the scene. Grief-stricken, Allen was approached by the Millennium Earl, who offered to resurrect him. Desperate to have his father back, Allen agreed. However, the resurrection transformed Mana into an Akuma, and the sudden realization of what had happened sent him into a rage. Before Allen could fully process it, Mana cursed his foster son—slashing Allen's left eye and leaving a pentacle scar while simultaneously granting him the ability to perceive Akuma with that same eye. Allen's anti-Akuma weapon awakened in response, and he quickly destroyed the Akuma form.
In his final moments, even as he was being destroyed, Mana told Allen he loved him and thanked him for correcting the mistake he'd made. It's one of the series' most tragic turning points, fundamentally shaping who Allen becomes.
Content compiled by AnimeList.moe from publicly available sources.
