Mafuyu was adopted by Tomo's father and decided to protect Tomo to repay her father for adopting her. Mafuyu and Tomo have been friends since childhood because of this, Mafuyu is very protective of Tomo and won't let anyone harm her, verbally or physically. Tomo has a habit of playing with Mafuyu's breasts, though they are very small compared to Tomo's. After the Time skip, Mafuyu's breasts grow and become equal to if not bigger than Tomo's. Because of the Sword of Maria's power, Mafuyu's breasts begin to grow, from a B-cup to a G-cup in episode 10.5 puts on her bra and Tomo says that it is too tight.
In the beginning, they were both very cold to each other, but later on they slowly opened up to each other. There were hints that they both liked each other such as Mafuyu getting jealous over other girls and Sasha always being protective of her. Before Sasha leaves they go on a date and it ends with both of them giving each other their first kiss. In the beginning, Sasha did not give importance to Mafuyu, calling her flat-chested. But after Mafuyu's breasts begin to grow, he starts paying more attention to her and started taking a liking to her. Both of their emotions begin to form into love.
Mutsumi Sendou was the first Maria of Sasha. In her first encounter with Mafuyu, she ridicules Mafuyu saying she has no breasts. Then, she plays with them, causing an awakening of the Sword of Maria. In five episodes.