The special Pikachu character who lost its electrical ability is named Peakychu.
Peakychu is one of several distinctive Pokémon encountered during Pokémon Pokopia’s story. Its name is a character-specific nickname, separating it from the ordinary Pikachu species that can also appear in the game.
Other named characters include Mosslax, a Snorlax covered with moss and plants; Smearguru, an unusually talented Smeargle painter; and DJ Rotom, a Rotom possessing a stereo system. These characters give the restored world personalities and story roles beyond ordinary habitat encounters.
Peakychu can be confused with Pikachu because the character is still a Pikachu. The question asks for the individual character’s special name, not the species name or the ability it has lost.