Tsukuyomi[ツクヨミ, Tsukuyomi]?, real name unknown, is a pivotal character in Oshi no Ko. She is a seemingly supernatural being inhabiting the body of a young girl and implied to be the one who reincarnated Gorou Amamiya and Sarina Tendouji as Aqua and Ruby Hoshino.
When Aqua momentarily gives up on avenging his mother, she approaches Ruby and reveals to her the truth regarding the deaths of her mother and Gorou Amamiya, prompting her to go down the same dark path as her brother.