Mari Tsutsui is a supporting character in the anime and manga series Whisper Me a Love Song. She is a third-year high school student and the drummer for the band SSGIRLS. Mari is known for her small stature, red hair styled with blunt bangs, and pink eyes. She has a distinctive habit of addressing people by their full names. Her birthday is June 8, and her blood type is AB.

Mari has an elegant and somewhat tsundere personality. She often appears composed and graceful but can show a prickly or reserved side, especially with people she does not know well. Beneath this exterior, she is deeply loyal to those close to her, particularly her childhood friend Kaori Tachibana. The two are almost always seen together, and Mari's bond with Kaori is a defining aspect of her character. Her motivations are rooted in supporting her friends and contributing to the band's success through her drumming.

In the story, Mari serves as a steady presence within SSGIRLS, providing rhythm and stability to the group's performances. Her role extends beyond music, as she also offers quiet support to the main characters, Himari Kino and Yori Asanagi, during their romantic development. Over the course of the series, Mari undergoes subtle growth, opening up more emotionally and learning to express her feelings more directly, moving beyond her initially guarded demeanor. Her notable ability is her skill as a drummer, which makes her an essential member of the band and allows her to express herself musically.