Ґаен Ідзуко

She is a young-looking woman who wears clothes that are too large for her. Izuko often boasts about her knowledge, coming off as somewhat arrogant. She claims to know everything, to the degree where she can predict the future; as a result, she likes to brag about this with her catchphrase, "There is nothing I don't know, I know everything." Izuko is also the younger sister of Tooe Gaen.

When others get help from her, she wishes for something in return; usually ending up with them doing her a favour.

She was the senpai of Oshino, Kaiki and Yozuru in their university years.

It is implied that, while creating Yotsugi, Izuko was cursed with knowledge.