Mahoro is a small girl with dark brown eyes, straight brown hair styled into pigtails with dark pink bubble-shaped bands, and a small patch of freckles in the middle of her face. She wears a pink dress with dark pink overall straps and buttons over a black tank top, and white sandals with a pink stripe wrapping around the sole, and dark pink flower decorations at the sides. On her left wrist is a bracelet with a floral charm, identical to the one her brother wears. She also wears a large sun hat with a dark pink scarf and bow at the crown and a light pink stripe at the rim.
Mahoro is a very stubborn girl who's very quick to judge others. Due to her mother's death and her father's work-related absences, Mahoro has grown extremely protective of her brother Katsuma. She also developed a greater appreciation for her father, and at the time he was the only person she saw as a hero.
She purposefully caused trouble for Class 1-A in order to prove to her brother that heroes aren't as great as they appear to be, as seen when she sends Katsuma to call for help only for them to arrive and discover a hologram of a monster instead of an actual threat. Later on during Nine's invasion of the island, she calls out for help as he approaches them to steal Katsuma's quirk and they are saved by Izuku, but when he was about to be killed by Nine, she frantically creates an "S.O.S Hologram" calling for more help.
Towards the end of the film when Katsuki and Deku are left heavily injured from Nine's attack, Mahoro begins to cry and calls out to them to keep fighting and not give up showing that she has grown to care more for the heroes. At the end of the film, Mahoro and her brother run down the deck at the harbor and happily wave goodbye to the heroes while thanking them for saving them during the attack, showing that she has now grown to appreciate them. 
- Mahoro’s given name contains the kanji “真” (ma, lit. “truth, reality, genuineness”) and “幌” (horo, lit. “canopy, hood”). Mahoro’s last name means island (島 shima).
- The part in Mahoro’s name “horo” is the Japanese pronunciation of hologram, her quirk.