Mayu is a student who is a huge fan of the idol group C.H.A, of which Harada is a member. She is a happy go lucky girl who is also a bit of a klutz. She came to the Viginti realm which is run by Ginti where Harada was waiting. Both were made to play a game of Twister that would decide their fates, and during the deadly stages of the game she learnt that her death was what would be called a freak accident, where while entering the bath she slipped on a bar of soap lying on the floor, hit her head and died instantly.

After the game both she and Harada gave a the arbiters a rousing performance, though Harada has already passed on, she continued to loiter around Viginti, where it is suggested that she has become an arbiter, much to Ginti's chagrin.

By the end of the series Ginti casts her and Harada into the void.
(Source: Death Parade Wikia, Anime+)