The athlete of the group, Mamoru is always trying to get her brother to play sports with her. She is sometimes mistaken for Rinrin due to their similar hairstyles and their penchant for donning their eyewear on their head.
As she is a tomboy, Mamoru uses phrases and mannerisms that only boys are expected to. As proof of this, she addresses her brother as Anii (あにぃ?), a shorter address used by a male teenager. In English, she calls him "Big Bro". Her birthday is October 18, is a Libra and stands 150 cm (about 4' 11") in height.
As the Athlete of the group she is usually doing a sport or exercise. She is seen swimming in the pool, running, or playing a sport.