Makki is a waitress at a café in Mosaic City's Shinjuku.
Her name "Makki" is actually not her real name, merely a fake identity. Her Servant Tsuda refers to her as "Yukika-dono". She is mentioned as being a survivor of the Fuyuki War, and is hinted as being an alternative, older version of Yukika Saegusa, another hint as her Servant's true identity due to the friendship the two shared in other timelines.
She started being an agent and Nightwatcher ever since the formation of Mosaic City, assisting Chitose Manazuru. This makes Makki the senpai to Erice Utsumi. Prior to her return, Makki used to be working alone conducting expeditions outside Mosaic City (which is said to be uninhabitable due to the post-war conditions) but recently returned to help Caren Himuro with issues surrounding the Command Seal Hunt incident. Caren Himuro gave both Erice and Karin an explanation on how Makki could go outside and come back unscratched and it was due to her ability to "avoid dangers" and survive Fuyuki for long periods. Since her return, she inherited the Shroud, a relic passed down to her by Caren Fujimura after her death and has been the user since. In addition to her agent job, she was also the manager of the cafe. Makki resents Caren Himuro for recklessly working her while wearing a maid dress because of it.
While looking at around her twenties, she was actually a whole lot older. Erice assumes her age to be around 40 to 50 years old.
Makki was seen to be uncaring and stoic at first, but further interactions with Erice softened her up and she starts warming up to both Erice and Voyager, but still however reluctant to speak anything that seems to involve Erice and her actual identity. Makki was also knowledgable that she immediately found out that Voyager cannot spiritualize himself due to Erice's ability and nature.
She also knows a lot about Erice and her family, especially her parents, which she owed them a favor for letting her into Mosaic City when she was still outside wandering around the ruins. She was also highly aware of Erice and her nature but refused to let her know everything, often cut her short.