A very friendly, polite, and carefree girl serves an important role as one of the royal guards in the Lunarian Kingdom, ranked as the 4th. She has a love for cute things, such as bunnies and plushies. Yuusei is not very fond of wearing her armor. Though she is friendly, there are rumors circulating that she can be scary or frightening. Additionally, she has a one-sided crush on Bibi, who is currently unaware of her feelings for them.