Kaguya (輝夜) is a young girl who found Ryōta Sakamoto at the shore and a member of an alliance called Sanctuary.
Kaguya is a young, cute girl with short hair. She has 2, pale green, rose hair pins on the left side of her head that ties a short side ponytail.
She has white and green striped knee socks, a dark green skirt with black layered frills, and a light green blouse. 
Equipment and skills
- Drawing tablet 
Kaguya is mute or at least has never been observed speaking, although her mentor Toshiro Amakusa seems to understand her well enough. With other people, or at least with Ryōta Sakamoto, she seems to be limited to communication by writing (often on her tablet) and by her gestures and actions.
Kaguya is believed to be capable of seeing and communicating with the spirits of dead people, but it seems to take a toll of her. She has claimed to dislike seeing murdered people, implying that she has some choice on whether she does.
- Kaguya is the youngest known real life Btooom! player.
- The name Kaguya means "radiance, shine, sparkle, gleam, twinkle, glitter" (輝) (kagu) and "night" (夜) (ya).
- Btooom! Manga Cover 13
- Btooom! manga, chapter 69, page 37
- Btooom! manga, chapter 69, page 39