Aki Masuzu is from Ehime Prefecture, like prefecture as Iyojima Anzu and Doi Tamako. During the initial Vertex Invasion, she guided them with her Miko abilities in using their Hero powers to protect the evacuating citizens. They took refuge in a school building among other people, where the three got to know one another better.
She is in constant contact with the Shinju but often complains about her duties (such as bathing in the waterfall to purify herself).
Masuzu is a pale-skinned teenager. Her hair is in a braid in the shade of khaki. Her eyes seem to be a dark brown and as Miko, she wears her red dress and white haori.
Masuzu is a childish person, often breaking small rules to have a little fun. Despite this, she cares deeply about her juniors, and often states her role is the "senpai".
As a miko, she is able to see vertex attacks, their numbers, and guide the heroes to sacred weapons before weapons were added to the terminal.
She is also skilled in mahjong.
Masuzu was introduced as bathing in the purification waterfalls alongside Hinata, and loudly stating her distaste for it. She was mentioned to have guided Anzu and Tamako to their weapons in the initial vertex attacks.
Masuzu appeared again during Anzu and Tamako's funeral, breaking down in tears and regretting not hanging out with them more often.
Masuzu lives in the complex with all the other mikos. She is roommates with Hanamoto Yoshika, and despite being her elder, is constantly breaking rules in secret and acts more like a junior.
When she received news of Anzu and Tamako's deaths, she went into a deep depression. Yoshika managed to talk her out of her grief, and Masuzu went to regain items from their rooms at Marugame Castle, starting her journey towards acceptance.
She seems to care greatly for Tamako, she led her to her weapon back in the early vertex attacks. When she attended her funeral she was sobbing her eyes out for her and Anzu.
She seems to also care for Anzu as she has also guided her to her weapon and cried at their funeral together. At one point, Anzu gave her a book, and Masuzu purposefully looked for it to read through after her death.
- A running gag in Uesato Hinata is a Miko is that Masuzu is the only miko who knows how to play mahjong, and constantly tries to get other people into it. As of chapter four, she has managed to rope all the mikos (save for Yoshika and Hinata) into a mahjong tournament.