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.
During her teenage years, she has a short hair and wears a standard seifuku. 
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 also considers herself confident in her job and even describes her performance as top-notch and having more drive than anyone. She is also sets a goal for herself, even telling herself that she needs to catch up to a movie heroine - a spy who wear bicker jacket and glasses. 
She always show her "strict" side when trying to reprimand Ayatsuji when he does as he pleases but constantly struggles to get Ayatsuji to follow protocol. 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 Division for Unusual Powers 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 Division later in life. 
Five years ago, Tsujimura's mother was supposedly killed by Ayatsuji's ability as one of the 17 accomplices in the serial murders in the Reigo island. 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 Division 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. 
- 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 favorite movie line is "Your biggest mistake was being born in the same era as me." 
- Tsujimura's mother taught Kyōka Izumi's mother how to transfer ability to a blood relative.
- The real life author's inspiration for writing mysteries stems from Yukito Ayatsuji's writing.