Kimihiko Kimizuka (君塚君彦 Kimizuka Kimihiko?) is the main protagonist and one of the main characters of The Detective is Already Dead. series. He is an 18-year-old high school student who became Siesta's assistant after a hijacking incident four years prior to the main story. After Siesta died, he wanted to start living a lethargic life. Until he receives a request from Nagisa Natsunagi.
Kimihiko is an 18-year-old high school boy with an average look. He has short black hair with slightly long bangs and has amber, golden eyes. Kimihiko is normally seen wearing a black suit and a white shirt under.
Kimihiko is known to be a magnet for trouble and because of this, he's able to think things clearly even in the most perilous of situations.
According to Siesta, Kimihiko is not suitable for combat and his stamina is weak.
According to Siesta, Kimihiko is very intelligent, but still inferior to her.
- Kimihiko means "lord, ruler, sovereign" (君?) (kimi) and "young man, elegant, handsome" (彦?) (hiko).
- Kimizuka means "mound, hillock, cemetery" (塚?) (tsuka/zuka).
- Nigozyu stated he once tried to give Kimihiko the code name "Kurokage (黒影 Kokuei?)" 
- In the Anime he has Brown hair in the Light Novel he has Black hair