Mahiru Koizumi

Mahiru has fair skin with light freckles flecked across her cheeks. She has vivid red hair cut in a short, smooth bob, with choppy bangs. Her eyes are a rather dark olive green. She wears a white uniform dress shirt with short sleeves and a chest pocket, with a red-and-white plaid tie at her collar. On top of this, she wears an olive green school jumper with a pleated skirt. Her legwear consists of a darker olive knee-high socks with lighter colored lines running around the cuff, with olive-black flat sneakers with white laces and soles. Her former school's symbol can be found on her shirt's sleeves, her jumper's chest, and her socks' cuffs. Mahiru can be seen with a black digital camera, appearing to be modeled after a Canon product, but with no discernable specific brand. It is hung around her body with an orange strap, a thin yellow line running through the center, attached with silver buckles.

During her high school years, she wears the standard Hope's Peak Academy uniform with black knee-high socks and the same shoes she wears during the Killing School Trip. Her hair appears to be slightly shorter and thinner.

As a member of the Ultimate Despair, she wears a white, short-sleeved, collarless t-shirt with a pair of denim shorts and thigh-high socks of a dark color. She appears to be wearing the same shoes as she wore in her first appearance. She is equipped with a black photography satchel that is hung around her body, and the same camera that she usually carries around with her on the daily.

Her swimsuit in Danganronpa S: Ultimate Summer Camp consists of a blue and white polka-dot bikini, a halter neck top styled with a knotted bow at the front, and matching high-cut bikini bottoms. She also carries her camera with an orange strap around her body, much like she did during the Killing School Trip.

Mahiru is a sensible and optimistic girl who is generally rather calm and unafraid to speak her mind. She initially comes off as confident but is later revealed to have self-esteem issues. It is evidenced by Mahiru's constant comparing of her photographs to those of her mother, a famous war photographer whose career led her to be absent from home for much of Mahiru's life. However, she finds it frustrating since others too always compare her style to her mother's, and that despite her love for photography, she feels her title is stupid compared to her classmates.

Meanwhile, unlike her successful mother, her father was a very poor parent, leaving the responsibility of the housework entirely to her. This is one of the main reasons why Mahiru has high expectations of men and is quick to be abrasive toward them due to having to take care of her dad growing up, preventing her from pursuing her dream of traveling the world to take pictures of people's smiles. An example is when she immediately labeled Hajime as "Unreliable Hajime" after he passed out upon being transported to Jabberwock Island, saying it would be hard for him to change her mind unless he mans up enough to protect the girls. When Hajime was being scolded by Mahiru, he likened it to being yelled at by his mom. However, when men meet her expectations, Mahiru is willing to reevaluate her first impressions. She upgraded Hajime from 'Unreliable Hajime' to 'Sometimes Helpful Hajime' after he handed her a magazine she needed. Despite initially opposing the idea of the Ultimate Imposter (disguised as Byakuya) becoming the group's leader, she was genuinely devastated by their death. She even once remarked that Nagito seemed like he would make a good stay-at-home dad.

Mahiru is much more tolerant and friendly to girls. In the original Japanese, she refers the girls in her class with their first name and "-chan" honorifics, while she refers the guys casually with their last name only. The subjects of her photos are usually of girls and explains that she easily gets bored of photographing guys. She loves taking photos of people's smiles, and it's revealed in her Free Time Events that she recorded everything in Jabberwock Island so that they won't forget, except for the guys which she only recorded once every three days. She also seems to have a playful side as she enjoys teasing people like Hajime by taking pictures of his "stupid" or "weird" faces.

Mahiru is also known for being protective, loving, and incredibly tolerant, especially towards girls, which is demonstrated by her friendship with Hiyoko, Mikan, and Ibuki. With Hiyoko, although they are the same age, Mahiru treats Hiyoko like a younger sister and becomes very close to her, even teaching her how to tie her sash. Mahiru shows much patience and kindness with Hiyoko, despite Hiyoko's clinginess and frequent immature behavior. As a result, Mahiru becomes Hiyoko's favorite and one of the few people she genuinely loves and respects and vice versa; she even starts calling her "Big Sis." Since Mahiru is so tolerant, she becomes close friends with Hiyoko even though Hiyoko has terrible manners most of the time. Mahiru, unlike Hiyoko, is extremely kind to Mikan since she knows how shy she is. Mahiru expresses more concern for Mikan than anyone else, although she is also surprised by everyone else's clumsiness. Mahiru says Mikan takes "skill" to tumble into awkward poses. When Mikan fell into a compromising position, Mahiru would try to cheer her up by telling her to be careful next time; she would also be furious at anyone who made fun of her or threatened her. Due to Mahiru's attentiveness towards her, Mikan commented how well Mahiru takes care of others. She also gets along well with Ibuki, who has a contrasting personality with her, even stating that she wanted to take pictures of her while jamming on an instrument.

Mahiru wants to help as many people as she can, but it'd be a mistake to call her a pushover. She doesn't hesitate to scold those who are rude to her and despite her complaints, she does really good at taking care of people. Due to her upbringing, she is highly perceptive when it comes to others neglecting their well-being, regardless of gender. She quickly notices details such as Kazuichi's soiled jumpsuit and Hajime's dirty sleeve, even offering to wash it for him. She also frequently worries about Mikan's clumsy behavior and, notably, offers to help Hiyoko tie her sash. She's also a highly empathetic person even caring about those who treated her poorly as shown by her utter regret over Natsumi's murder and trying to make amends with Fuyuhiko despite both of them mistreating her. Even though she was upset with Nagito for what occurred to Teruteru and the Ultimate Imposter, she was the first to bring him food and worry about him being chained in the old building.

When confronted with injustice, Mahiru's sympathetic character, raw emotions, and unwavering sense of justice are on full display. This is demonstrated when she finds the body of the Ultimate Imposter and allows her grief to drive her resolve to uncover who murdered them. Another example is when, despite Fuyuhiko's reputation for aggression and violence, Mahiru confronts him about Sato's death and tells him that vengeance is wrong for whatever reason. This is all the more striking when one considers that by that time, Mahiru still had her school memories of Sato erased and relied solely on the information presented in the game.

From a young age, Mahiru was inspired to become a photographer like her mother, who was a famous war photographer. Despite being young, she won numerous photographer awards and became famous for her skill at taking portraits. Mahiru's core belief as a photographer is photos depict everything. Whether it's beautiful or horrible, it's the duty of a photographer to keep taking photos, which is why in any kind of situation, Mahiru doesn't mind snapping photos. However, Mahiru isn't fond of selfies and rarely takes pictures of herself. She also has no interest in still life photography, as she believes that "proper subjects have to have facial expressions".

Even though she specializes in multiple photography categories, Mahiru's favorite involves taking portraits of smiling people. She could take a perfect shot of someone's smile and according to Hajime, he never saw someone smile so bright and heartwarming until he saw Mahiru's photos. Traveling the world and capturing the joy on the faces of people from different backgrounds has long been her dream as well. In Island Mode, she states that she enjoys ambient and picturesque places, as they can naturally make people smile. Despite that, she expressed her dislike towards boys by not taking many pictures of them.

Compared to her mother's theme, Mahiru's is considered too conventional and many people don't really care to judge it and expect her to take pictures of different objects, as they believe that she could produce more "amazing" results. She became tired of receiving constant insincere compliments to her photos, such as "amazing" and "awesome". This is why Mahiru felt both bashful and touched when Hajime said that looking at her photos let him "realize what's actually important in front of you." As a result of this remark, Mahiru was grateful that Hajime tried to take her picture during her last Free Time Event per her request, even though the result was "goofy," according to her. The shot remains a favorite of hers, and she went so far as to say she likes it as much as photos her mom would take, complimenting it as "a record of myself as you see me," mirroring Hajime's heartfelt comment.