Little is known about Maruta's relationship with Mei, other than the fact that they both are on school council together. She appears to be somewhat afraid of Mei.
Maruta routinely reprimands Yuzu on her informal appearance and constant negligence of the school rules.
Maruta and Momokino are often seen having one-sided conversations about Yuzu's bad behavior. They are both on the school council.
There is very little interaction between Harumin and Maruta, but from volume 1's extras, it appears that Glasses-Senpai has a crush on Harumi. Harumi was the one to nickname her "Glasses-Senpai".
As seen on volume 5's extras, Maruta and Mitsuko have a good relationship, which Maruta being seemingly the only person not afraid of Mitsuko. Maruta constantly teased Mitsuko due to her true childish self compared to her mature persona, and due to her love for her little sister, as Harumi feared Mitsuko's personality. It's possible she has a crush on Mitsuko. She also nicknamed Mitsuko "Micchan".