She has light cyan hair which is parted to the right, part of which she keeps in a ponytail. She wears a white neck scarf patterned with the same cyan hue, a white dress shirt, a gray suit coat which she keeps unbuttoned, and gray slacks. She also wears gray gloves, black heels, and a dark gray belt.
Tsujimura appears as a kind and genuine woman, though slightly gullible as shown when Ayatsuji tricks her in making him coffee.
Tsujimura is also very dedicated to her job and respectful to her seniors. She constantly struggles to get Ayatsuji to follow protocol, harshly reprimanding him when he does as he pleases. Feeling strongly about her duties, she often gets swept up at the moment.
Tsujimura's ability, Yesterday's Shadow Tag (きのうの影踏み, Kinō no Kagefumi?), allows Tsujimura to create 'baby shadows' and control their strange/curious lives. It also takes the appearance of a grim reaper like shadow creature with a scythe when it activates automatically.
Just like Kyōka, her mother transferred her ability to her. Therefore, she does not have complete control over it. It most often acts as an automatic response type ability that follows the command placed on it by her mother:
"Kill anyone who my daughter Mizuki Tsujimura tries to kill right before she kills them"
In other words, Tsujimura’s ability will activate immediately when she wants to kill someone and the body shadow will slaughter them faster than she can kill them. Thus, making Tusijmura unable to kill anyone herself. Tsujimura has no control over this function of her ability. Therefore, her ability itself is the one being judged by Ayatsuji's ability, Another.
Not much is known about Tsujimura's history, however it is known that she grew up having a complicated relationship with her mother who shared the same name with her. Her mother was largely absent from her life due to being a prolific and skilled agent with the Special Abilities Department and was always away on missions. The details of her father are unknown. Tsujimura largely considered her to be mysterious and has always wished to know more about her. During her childhood, Tsujimura watched detective movies, which inspired her to be a skilled agent when she joined the Special Abilities Department later in life.
A couple years before the events of Gaiden, Tsujimura's mother was supposedly killed by Ayatsuji's Ability as one of the 17 accomplices in the serial murders on the island of Reigo. Shortly after this event, Tsujimura's Ability Yesterdays' Shadow Tag activated. Her mother's murder by Ayatsuji's Ability was what influenced her to join the Special Abilities Department and take on the role of monitoring Ayatsuji's case in order to know more about what happened to her mother and more so who her mother was as a person.
As a means to return his debt from Ango from the past, Chuuya tells Tsujimura that her Ability was "not hers", explaining that it was an automatic type response type and that it "reeked of death", indicating it had killed a high number of people, which was highly unlikely for an Ability that had only supposedly activated a couple years ago. He encourages Tsujimura to remember who died when her Ability activated to give her a hint of the true origins of her Ability. Tsujimura then realizes that her Ability originally belonged to her mother.
Tsujimura's mother has a meeting with Ayatsuji to discuss the details of the case Tsujimura had been following and how Tsujimura had been doing in general. Tsujimura's mother was revealed to be alive and was never killed by Ayatsuji's Ability. The truth was she had become much too prolific and had gained too many enemies and had to fake her own death in order to go into hiding and this was accomplished by her teaming up with Ayatsuji. Tsujimura's mother now works in the deep shadows of the Special Abilities Department as an agent who can never appear on the surface.
- The name Mizuki means "deep" (深) (mi) and "moon" (月) (tsuki/zuki).
- Mizuki's surname Tsujimura means "street, crossroad" (辻) (tsuji) and "town, village" (村) (mura).
- Tsujimura's mother taught Kyōka Izumi's mother how to transfer ability to a blood relative.
- The author's inspiration for writing mysteries stems from Yukito Ayatsuji's writing.
- Bungo Stray Dogs Manga: Chapter 43.