Izumi is of average height and has a slim figure, described to be relatively handsome and attractive with a slightly feminine-looking face. He has deep blue eyes, messy black hair that goes down to his nape with parted bangs, and pale skin. He appears to have fairly sharp canine teeth, a lip and many ear piercings, and a few minor tattoos on his left shoulder, upper arm, and side.
In his first appearance, Izumi is seen dressing heavily in order to hide his tattoos, wearing his winter school uniform and blazer. He kept his hair shoulder-length and straight to avoid drawing attention to his piercings and wore thick-rimmed glasses.
Out of school, he dons a more casual appearance, removing his glasses and keeping his hair tied up into a small ponytail with a few bangs framing his face, seemingly indifferent about the fact that other people could see his piercings and tattoos. He wore a lip ring and chain, along with a striped t-shirt, a short-sleeved jacket, and various bracelets.
After cutting his hair and withdrawing from wearing glasses in Chapter 26, Izumi's piercing holes become visible, but it is noted that a few piercings, including the one on his lip, closed up as a result of not using them. His new appearance sparks the attention of many, and he is considered to be quite attractive by the girls in his class, much to Kyoko's annoyance. He is seen wearing his blazer fully buttoned up less often, opting to wear the school sweater over his uniform instead.
In school, he gives off an impression of a quiet, anti-social guy. Usually assumed to be an otaku with good studying capabilities, Miyamura is soon to be viewed as a good friend to Hori Kyouko and her closest friends. Despite the weather, Miyamura tries to cover up as much as possible in order to hide his tattoos and leaves his long hair loose to cover up his piercings. This image briefly changes once he leaves school, particularly at Kyouko's house. Once he is outside school, he removes his blazer and necktie and wears his hair up which visibly shows his multiple ear piercings. He also enjoys getting lattes from Starbucks and does not mind wearing short sleeves that shows off part of his tattoos. Unlike most characters that wear glasses, Miyamura does very poorly in his studies, only managing to score full marks in P.E and average (or below) in all other classes. Although usually having trouble pronouncing certain Japanese words, he is very good at tongue twisters.
Miyamura generally has a laid back attitude and is slow to anger towards the friends that he met at Katagiri High School (with the exception of Sawada) but shows that he has a short tempered and violent side especially towards his ex-classmate, Shindou. During his junior high years, he pierces his ears using a safety pin as a way to cope with his struggling school life where he is ostracized and bullied by his classmates for his shyness. During this time it is suggested that he also contemplated suicide. It is unknown where or if there is a specific reason he got his tattoos but it is said that he has a fairly impulsive nature and the tattoos were gotten on impulse. When Hori Souta suggests he gets a pair of wings tattooed, he agrees that it is a good idea although he doesn't follow through with the tattoo in the end. He does not seem to regret getting the tattoos, however, he needs to keep them covered up and because of this is unable to wear short sleeves or a swimsuit while in school. His family runs a bakery and he can be seen helping out occasionally after school when he is not spending time with Kyouko, Ishikawa Toru, or Shindou Kouichi. He is very good at making desserts, especially cakes.
He appears to have very low self-esteem and is very awkward when talking to people he's not close with, often saying he can't connect well with others. He worries that it would be embarrassing for Kyouko to be seen with him. Miyamura hates drawing any sort of unnecessary attention towards himself, preferring to be treated as "invisible" in class. However, because he feels that Hori is being made fun of for dating him because of how he looks, which leads him to cut his hair, and also stopped him from wearing glasses to school. This causes a lot of girls to start approaching him and commenting on how good looking he is, even flirting with him and snapping pictures of him with their phones much to Kyouko's annoyance.
He is a very kind and caring person, an example may be when he brought Souta back home after Souta tripped and got a nosebleed. Miyamura also cares a lot for his friends and has been shown multiple times helping Kyouko out and picking up Souta from school. He is also very air-headed and clueless, especially when it comes to romantic affairs which leads to comical situations. Despite his mellow nature (Shindou excluded), he becomes violent when trying to defend himself from physical attacks and has become violent on two separate occasions, once when the student council tries to make Hori apologize for something that was not her fault but actually Remi's fault (he headbutts Sengoku Kakeru which leads the student council president to become rather afraid of him), and when Toru argues with Miyamura about Kyouko's feelings towards Miyamura. He also holds a very short fuse when interacting with Sawada Honoka, easily becoming annoyed by her presence and antics.
He is very afraid of anything related to horror or gore but usually watches horror movies because Hori enjoys them. It is unknown if he is a sadist or a masochist, however he often hits Shindou and aims sharp remarks towards him, especially regarding the fact that Shindou had to repeat a grade due to poor attendance. He does not seem to hold any sadistic feelings towards his girlfriend except that one time he decided to put his foot on her head because he wanted to bully her back for once since he is the one always getting pushed around. In fact, he has problems treating anyone impolitely or violently towards anyone except Shindou or occasionally Sawada.
Back in middle school, he was always ignored and left out. One of the people that constantly "played" with Miyamura to provoke and bully him was Tanihara Makio. During group discussions he has blatantly ignored his other classmates, as they thought of him to be someone "boring", "weird" and "too gloomy" to hang around, therefore he had no friends. Throughout his elementary school and middle school days, many classmates of his spoke behind his back remarking how it's his own fault for not having friends and being so silent, and even though he is not necessarily a "bad guy" he's weird and shady.
As Miyamura did not know how to deal with the bullying, he started using clothing pins to pierce his ears to help him cope with the pain he felt about being lonely and "hated" during middle school when he was being bullied. This then becomes the reason why his long hair in high school (to cover the piercings). He also has gotten tattoos to relieve the stress he felt in middle school which covers up by wearing multiple layers of clothing.
One day after class, someone bumps into him causing his books to scatter all over the ground. This is when he meets Shindou Kouichi. Shindou picks up Miyamura's notebooks, then calls him by his name wrongly which annoyed Miyamura. After this encounter, Shindou began to take interest in him and started pestering him ever since. After a while, they soon became good friends. Even though Miyamura still thinks Shindou is pretty annoying, they are still both quite close friends to this day.
The story begins when Miyamura handing Kyouko an eraser, which she dropped. As he walks away, Hori's friend Yuki tells her friend that, Miyamura seems really dark, and that he's probably an Otaku (this is due to the appearance he has at school). Later that day, Miyamura, who is now wearing his hair up and has his piercings, walks home Souta Hori after running into him when Souta gets scared by a dog. Upon reaching the Hori Household he is invited inside for tea as a thank you for taking Souta home, during some small talk between Miyamura and Hori, Miyamura casually mentions Hori's name much to her shock. After a petrified Hori asks if Miyamura is from her school, he tells her that he's Miyamura from her class. This shocks Hori as the Miyamura she knows from school and the one in front of her looked very different. Also, Miyamura has now seen her without make-up which even her best friend, Yuki, hasn't seen her without.
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He is shown to value Hori as a very good friend and in turn, she values him too. She is, according to Miyamura's mother, one of his only friends since Primary School. As the story progresses, he starts developing feelings for her. In chapter 20, when Hori is sick and lying on her bed trying to sleep, he says "I like you" when he knew that Hori is actually awake and listening. He loves Hori's company and when asked by Hori's father to cut his hair, he did not hesitate to, before being stopped by him. She is the main love interest of Miyamura.
She is the first friend Miyamura has made since high school has started. Hori first met Miyamura in his outdoor style, when he brought Souta home after he fell due to a scary dog, but they also met during the beginning of their first year when Miyamura was with Shindou. At first Hori didn't recognize that he was Miyamura, a classmate, but when she invited him into her house he unexpectedly called out Hori's name. Hori was surprised that he knew her name, and when he said he was Miyamura. From that point on, they became friends, and Hori has been friendly and open to him even though of his appearance. He often visits Hori and Souta at their home,and brings cake from his family bakery. Hori was the first person from his high school to see Miyamura in that appearance, and he was the first person to see Hori in the "housewife" appearance. They wanted their "secret" appearance to be kept secret and that only each other knew what their other self was like. As the story progresses, they realize they like each other, and Hori becomes Miyamura's girlfriend. In chapter 37 on a rainy night, when they are alone together in her room she realizes how much she loves Miyamura and they decide to sleep together that night. After the realization sets in for Hori that they might be separated after this last year of high school, she tells him she still wants to be with him. Miyamura , in turn,asks Hori to marry him. As of now in the manga, they are engaged.
He refers to Miyamura as 'onii-chan' and often clings to him when Miyamura comes over. He is a fairly independant and observant child, staying out of the house to try to let Miyamura and his sister spend more time together. He seems to have some knowledge of sex as he asks Miyamura if Miyamura and Kyouko were always doing 'that' after finding his school pin on the floor. He is a picky eater but has since learned to be less picky thanks to Miyamura's influence and encouragement for him to try new things, but still dislikes carrots. He is very protective of his big sister, Miyamura, and the roles they play in his life.
Kyousuke is often excited about having Miyamura over and greatly enjoys his company. He supports the relationship between Miyamura and Kyouko and refers to Miyamura as his 'heir'. Even though he likes Miyamura a lot he had some trouble recognizing Miyamura when he has his hair down and glasses on or when he cut his hair short. Miyamura prefers Kyousuke's company compared to the company of the other girls in his class who started taking notice of him after he cut his hair short. Miyamura refers to Kyousuke by his first name. It should be noted that Kyousuke has forced Miramura to bath with him, thus scaring him emotionally.
He is surprised at how young she is when he first meets her. She takes a great liking towards him and encourages the relationship between Miyamura and her daughter. She also often prioritizes him over her husband such as preparing food and tableware for Miyamura but having none for Kyousuke. Yuriko is grateful to Miyamura for helping out with her son and daughter especially since she and her husband are both busy and often away from home.
He is Miyamura's first male friend in Katagiri High and is now one of his closest friends. He was hostile towards Miyamura at first because he was jealous of how close Miyamura had become with Hori who he had a crush on, but later in the manga, it is shown that he has changed his love interest to Yoshikawa Yuki. He is the only person in Katagiri apart from Hori that knows of Miyamura's tattoos or see Miyamura in casual clothing. At one point in the manga, they were trying to call each other with their first name, but the next day Miyamura forgot about that and addresses Toru formally as Ishikawa-san. After finding out Hori likes Miyamura he tries to get a response from Miyamura but ends up arguing with him. He is the first to know about Miyamura and Hori dating and cheers him on despite feeling heartbroken because he still liked Hori. After that, the two spent less time together but has since become close again. He is shown to be a good swimmer and worked part-time as a lifeguard during the summer. He likes sailor uniforms and after catching Miyamura wearing one once before asks if he will wear it again, then proceeds to imagine how Miyamura would look in a sailor uniform once his hair has grown out. He cares very much for Miyamura and sometimes worries for him.
Miyamura's best friend since junior high, he knows all there is to know about Miyamura. They share an interesting friendship where Shindou views Miyamura as a close friend and devotes 30% of himself towards Miyamura, while Miyamura doesn't hesitate to abuse and verbally attack Shindou. Miyamura is quick to drop his reserved and quiet demeanor around Shindou (even when there are other acquaintances around such as Toru and Hori) and shows a more darker, somewhat sadistic and cynical side of himself. After graduating from junior high it seems that they lost contact for a period of time, however recently they seem to be hanging out together more often and Miyamura often calls on Shindou for advice. Shindou occasionally refers to Miyamura by his first name.
- His name Izumi (伊澄) means "this" (伊) (i) and "clear" (澄) (zumi).
- Izumi's surname Miyamura means "temple, shrine, palace" (宮) (miya) and "town, village" (村) (mura).
- Izumi works in his family's bakery after school and wishes to continue the family business.
- Izumi is very good at tongue twisters.
- Izumi can't pronounce the words "atatakai" (meaning warm), "katatataki" (meaning shoulder massage), "yamabuki-iro" (meaning bright yellow), and "zashiki warashi" (a childlike guardian spirit), instead says "akkatai", "kakatataki", "mamabuki-iro", and "dashiki zarashi".
- Izumi's Japanese score is 2.
- Izumi had 10 piercings in total which two of them closed, one on the lip and one on the tongue.
- In Chapter 13, it is revealed that Izumi is afraid of horror movies.
- Izumi has a full mark in Health, which he usually uses against Toru.
- Izumi won first place in the Horimiya character popularity contest on November 17th.
- Izumi dislikes tomato peel.
- Izumi likes women who wear blazers.
- On the webcomic ending, Izumi and Kyouko had a son named Kyouhei.
- Izumi is an only child.