Yui Saikawa (斎川唯 Saikawa Yui?) is one of the main characters of The Detective is Already Dead. series. She is famous as an active idol and is frequently featured in magazines and commercials. In order to prevent the theft of her family heirloom, the Miraculous Sapphire, she requests Kimihiko and Nagisa to protect her and her heirloom.
Yui is a 14-year-old, junior high school cute girl who wears an eye patch over her left eye. She has long black hair with pink and white highlights tied back with two pigtails. While performing as an idol, her custom consists of a one-piece dress with a white top and shiny pink skirt, white leggings, and pink heels. When she is off stage, her outfit consists of a grey hoodie with what resembles bear ears, black shorts, and white sneakers.
Although Yui is the youngest in the series, she is said to be the most mature and has a strong personality.
Yui is the one, and only child of the wealthy Saikawa Family. She was blind in her left eye ever since she was born, making her feel shy as a kid. At some point in the past, her parents gifted her a sapphire-colored fake eye that is said to be bluer than any sea. Because of their gift, Yui was happy and became much more confident than before and she also started working as an idol around that time, with her parents delighting whenever they saw her on stage. Although she briefly had a wonderful time, Yui's parents, unfortunately, died in an accident three years ago, leaving her an outrageous amount of fortune and the sapphire-colored eye along with a huge house.
Yui is a very talented singer, said to possess unparalleled dancing sense and singing skills.
- Yui means "only, solely" (唯).
- Saikawa means "cleansing, purification" (斎) (sai) and "river, stream, brook" (川) (kawa).
- When Nigozyu was writing the manuscript, Yui was originally the Great Detective, and Siesta was a supporting character.