Midori is a petite girl with fair skin. She has long brown hair that is normally tied up in a high side ponytail. Her hair is hard to tame, so it often looks a bit messy. She has mentioned that she rarely wears her hair down because it looks like a bedhead. She has round, bright green eyes, and she usually has a cheerful expression. Because of her small stature and build, she is often mistaken for a junior high student, or sometimes even younger. She has been the shortest player on any team she has been a member of.

She can often be seen wearing her school uniform, which consists of a white dress shirt, a red bow, a tan sweater vest, a gray skirt, and shin-length black socks. She always wears shorts under her skirt. While playing for Karasuno, she wore the standard black and white uniform with the number 8. While playing for Niiyama Jōshi, she wore the standard white and red uniform, once again with the number 8. During games, she wears black knee pads, black elbow pads, and a black compression sleeve on her right arm. Her volleyball shoes are white with green accents. Her casual clothes often consist of cute, girly clothes with bright colors and patterns. She wants to wear shoes with heels, but she is often too clumsy to be able to walk in them.

Midori is often identified by her loud and energetic personality. She has a loud speaking voice that only gets louder when she gets excited, which is often. She is friendly and cheerful, and she talks a lot. She is said to be someone who never runs out of things to talk about. She can be very affectionate towards the people she is close to, and she is normally very straightforward with her feelings. She is often described as high-energy, and she is enthusiastic about almost everything she does. She is very optimistic, and it is unusual to see her upset for long. She has said that she almost never gets nervous, instead growing more determined when faced with adversity. She is naturally curious, which can sometimes get her into trouble. She can be very simple-minded and reckless, diving headfirst into situations without thinking about the consequences. She has an almost supernatural ability to persuade people and get what she wants, so she can be quite spoiled at times. She can also be a bit greedy. She is incredibly clumsy, often tripping over herself and dropping things. She doesn't do very well in school, and she can be quite oblivious, often saying whatever is on her mind without considering her surroundings.

She takes on a completely different personality in games. She becomes almost scarily serious, her cheerful expression traded for one of absolute focus. She is always 100% determined to win, and she believes wholeheartedly that no game is unwinnable. While still clumsy and full of energy, she moves with more purpose. She also becomes more crafty, coming up with clever ways to trick her opponents. She absolutely hates being underestimated because of her height, and she finds great joy in seeing her opponents' looks of disbelief when she scores on them. People have noted that the more experience she gets, the more devilish and almost sadistic she becomes in games.

When she was little, it was easy to tell that she was an active and energetic child. She was always doing things, always bouncing off the walls. This drove her parents crazy, as it was hard to keep her under control. It wasn't until her older brother, Ichirō, got into volleyball that she found a way to channel her energy. Her brother always played sports, but he never played volleyball until a friend told him he'd be good at it. Ichirō wanted to work hard to become the best he could on his own, so he asked his younger sister to help him practice. He had her toss to him over and over again until neither one could move their arms. During this time, Midori decided she wanted to be just like her brother and play volleyball. He taught her everything he knew, though all he knew was how to be a wing spiker.

Midori continued playing volleyball as she grew up. She was a naturally gifted player, so she had a bad habit of only relying on her natural talents. In junior high, she attended the powerhouse school Kitagawa Daiichi. She impressed the coaches, and she was put on the starting lineup as a first-year. This caused her to gain the attention of Isobe Kaede, the second-year libero on the team. Kaede disliked how Midori was given a starting position without having to do much work, while Kaede had to work hard and fight for her spot on the court. Midori was always praised for being such a strong player despite her height, but Kaede did not receive the same praise despite being similar in height. After losing a championship game, Kaede took out her frustration on Midori by saying that someone who only ever relied on their natural talent and never worked for anything had no right to be upset over a loss. Midori began crying, and Kaede immediately felt guilty. Afterwards, Kaede apologized to Midori, saying she should not have been so cruel to her when the younger girl did nothing wrong. Midori, however, took her works to heart and vowed that she would give it her all from then on. She wanted to show her senpai that she could work just as hard as everyone else, but she never got a chance to. After the end of that playing season, Kaede left Kitagawa Daiichi and transferred to Keisetsu Junior High, a well-known powerhouse school in Tokyo.

While in her second year, her brother, a third-year at Karasuno High School and a part of the volleyball club, developed an illness that led to the rapid deterioration of his eyesight. This led to his early retirement from the team. Midori swore to keep playing volleyball and become the best player in Japan to live out her brother's dreams. This oath, however, was put on hold for a long while. When she was in her third year of junior high, she suffered a severe ankle sprain that took her out of the game for months on end. All recommendations she had received for elite high schools were taken back because the amount of time it would take for her to fully recover would have been too long. She was in a slump for a while, but she quickly bounced back. She vowed to come back better than ever and prove to all those schools that she could still be the best player in Japan. She recovered much faster than anyone thought, and she was back in time for the first season of her high school career, where she attended Karasuno High.

For that first year, Karasuno's girls team had a poor record. Midori very clearly stood out from the rest of the team, but couldn't do much on her own. In the middle of the year, Aoyama Momoka, a first year setter from Shinzen High, transferred to Karasuno and joined the team. The duo of Midori and Momoka emerged, giving Karasuno a valuable weapon. Even still, they struggled to win games. They were eliminated in the first round of the Miyagi Prefecture Nationals qualifers, but the coaches from Niiyama Jōshi High had watched the game and recognized Midori's abilities. They offered for Midori to practice with Niiyama Jōshi's team after Nationals was over, and if she impressed the coaches, she would be allowed to join the team. Midori was incredibly nervous, despite almost never feeling nervous. She practiced with the team, made a good impression, and she transferred to Niiyama Jōshi for her second year of high school. She was reunited with Kaede, who was the starting libero for the team. Finally able to prove how much she had grown, Midori worked very hard and earned the title of Ace in her third year. In her third year, her team faced Fukurōdani (Maho's team) in the finals of the spring tournament, narrowly winning in the last set.

After graduating from high school, she moved in with Kageyama. She tried out for the V.League Division 1 team, the Hatsumichi Springs, becoming a wing spiker. Despite not growing much taller, she became known as Hatsumichi' Petit Terror (プチテラー Puchi terā). Maho and Midori were a powerful combination, and the way they seemed to be able to communicate without speaking led to them becoming known as the "witch and her familiar" (魔女と使い魔 Majo to tsukaima).

• Her favorite food is strawberry shortcake or any other sweet cakes.
• Current concern (2012): Upon meeting one of her classmates, he asked if she was a junior high student that had skipped a grade because she was smart. Everything about the question made her upset.
• Current concern (2018): She's excited for Kageyama to play overseas, but she also doesn't want him to leave because she'll miss him.
• Her star sign is Aries.
• She is one of the youngest people in her grade, her birthday being very close to the birthday cut off date for school registration.
• She likes to give people nicknames, usually by adding -chi onto a shortened version their name. She claims it's "cute," but many people have said her nicknames are just weird and embarrassing.
• Her favorite moment during a volleyball game is when someone on the other team comments on her height, and she spikes the ball right past them shortly afterward. She says it's "immediate revenge."
• She wears volleyball shorts under her school uniform, a habit she picked up from Kaede in junior high.