Atsushi Ōtani (大谷敦士, Ōtani Atsushi, lit. meaning "big valley") is the boyfriend of Risa Koizumi. He is the deuteragonist of the original manga, anime, video game, and movie, as well as a support character in the sequel manga.
Throughout the series, Ōtani would often act prideful and arrogant displaying a pseudo-Napoleon Syndrome especially when being praised in any manner. However he is actually a very kind and funny person. He greatly struggles with his short stature, which was made worse after his then-girlfriend, Mayu, broke up with him for someone taller. Ōtani has a very happy and carefree attitude when he is goofing around with Risa, and this is especially obvious when they are talking about Umibōzu or at an arcade.
Despite his short stature, Ōtani is an aspiring basketball player. Even after his final season, he continues to show up to the basketball club and cheer on his teammates, and was able to play a scrimmage with them one last time before graduating. Ōtani loves basketball so much that he studied hard to get into a good University to become a teacher so he can teach children how to play basketball.
Ōtani has a very gentleman-like personality when it comes to a woman who is upset, often assisting them in any way possible to cheer them up. This is seen when he gives up trying to date Chiharu so she can be with Suzuki and again when he is tricked by Hitomi Ōtani. Even though gorgeous Hitomi tricked him into spending the night at her house and attempted to seduce him, he never cheated on Risa and remains loyal to her.
Much like Risa, Ōtani is not very intelligent and is very naïve when it comes to love. It took several confession attempts from Risa and Nobu point blank telling him in Risa's stead for him to finally understand Risa's feelings. Ōtani is easily embarrassed when Risa is too open about her love for him and will not repeat himself if he says anything lovey to her, often hitting her on the head and calling her names out of his own embarrassment. He shows an extremely jealous side when it comes to Risa, becoming very frustrated at Maity-sensei, Haruka, and Kohori for showing affection towards Risa, yelling at Seiko for kissing Risa on the cheek, and almost starting several fights with other men trying to protect her. He later shows that he is not very confident in Risa's feelings for him and becomes depressed at the thought of her not loving him as much as he loves her.
Ōtani stands at only 156cm or 5'2" tall and is very lean muscled, being described by Risa as having a manly body despite his short stature. He can be found wearing a variety of fashionable clothing and having his hair down for everything other than basketball where his fringe is held out of his eyes with hair ties or a headband.
In the manga, Ōtani's hair is seen as the light red color as well as a vibrant orange and light brown, while his eyes are seen as both brown and reddish-brown. His summer school uniform consists of a white short-sleeved polo shirt with a brown stripe on the collar and a pair of brown dress pants. The winter school uniform consists of a mustard yellow plaid long-sleeved button-up dress shirt and a brown tie, suit jacket, and dress pants. Ōtani is occasionally seen wearing his uniform in the manga, like when he's trying to reach the box in the faculty office in Chapter 01, but he is usually seen wearing casual clothes because Maido Academy is uniform optional.
In the game, Ōtani's hair and eyes are both light orange in color. His fashion sense is the same as seen in the anime and manga, and the school uniform he wears is the same as the manga.
In the anime, Ōtani has light red hair and brown eyes similar to Risa's. Ōtani wears a school uniform consisting of a short sleeved white dress shirt sporting a pocket, red star, blue and red buttons/patches, with a blue and green striped t-shirt underneath, brown pants, and blue shoes. He is usually wearing a sweat band around his wrist. During winter weather he wears the same basic uniform, but the white dress shirt is buttoned up, he has a red tie on, and a peach cardigan with a red star and stripes over top.
- 9th Grade - Umibōzu Concert
The chapter primarily focuses on Risa's point of view.
Ōtani unknowingly first met Risa at an Umibōzu concert that fell on his birthday during their final year of junior high (equivalent to 9th grade). The chapter starts with Ōtani in a very depressed mood. Nobu asks what's wrong with him and Nakao replies that Mayu had recently broken up with him due to his obsession with basketball. This scene is followed by a flashback of Mayu returning her Umibōzu ticket to Ōtani, telling him she can't go to the concert and that there is someone else she is seeing now. Ōtani was initially going to tear up and trash the tickets, but decides to still go.
A girl approaches him while he is sitting in the back of the concert hall alone. Before she can speak, he starts to cry. The girl asks if he is okay to which he replies with a simple, "Yeah," before taking a phone call. The call is brief only mentioning to the person that he was alone, that it was his birthday, proceeds to call the person a dummy, thank them, and hang up.
The concert begins and the girl rushes out getting caught in the crowd, Ōtani grabs her arm and pulls her out of the mosh pit. She thanks him and tries to begin a conversation, but it is so loud that he can't hear her. The crowd and music suddenly go silent as she yells for him to "cheer up", which Umibōzu reciprocates telling to cheer up as well. The girl then yells to Umibōzu that it is Ōtani's birthday, the crowd and Umibōzu wish him a happy birthday. He talks with the girl about Umibōzu for a short while before she walks away.
Ōtani notices the girl looking for something and that her shoe is missing, he finds her destroyed shoe in the trash and returns it to her. Ōtani offers his shoes to her saying that he "don't need'em" and "with the mood (he's) in, (he) don't even want'em." The girl gives him some strawberry milk candy in return and wishes him a happy birthday once again before parting ways.
- Risa Koizumi: Risa is Ōtani's friend and classmate, and later his girlfriend. The series started with Ōtani and Risa as enemies, not wanting to be around each other as they were always being grouped together as "All Hanshin-Kyojin." Shortly after the series begins, Ōtani develops a crush on Risa's friend, Chiharu, and notices Risa also has a crush on a boy named Suzuki. Ōtani befriends Suzuki in order to form a pact with Risa to set each other up with their respective crushes. After a series of unfortunate events, Ōtani overhears Chiharu saying that he is so easy to talk to because she does not think of him as a boy due to his height. Shortly thereafter, Ōtani and Risa figure out that Chiharu and Suzuki have crushes on each other and decide to support the two of them instead.
- Following that, Ōtani and Risa decide the compete with each other over who can find a girlfriend or boyfriend first. Ōtani arrogantly believes that he will win because a lot of girls in the school already have a crush on him. As Christmas approaches, Ōtani and Risa find out that they both love Umibōzu and surprises Risa with tickets to the Christmas concert. Ōtani's ex-girlfriend, Mayu, shows up before the concert and asks Ōtani to join her and their old basketball club for a Christmas party. It didn't take long for everyone to figure out that she and her boyfriend had broken up, and that she intended to ask Ōtani out again, so Risa encouraged him to go to the party instead of the concert. Instead of going to the Christmas party, Ōtani holds true to his arrangement with Risa and shows up to concert stating that he had made plans with Risa first and that's all that matters.
- Several months later, Ōtani notices Risa becoming increasingly depressed and decides to cheer her up by showing her his secret spot to watch fireworks. Risa confesses to Ōtani that she is in love with him during the fireworks, but he considers it a joke and blows her off. After several more attempts at convincing him it is the truth, Ōtani finally understands her feelings. He takes a short time to think about it and tells Risa on their school trip to Hokkaido that he cannot suddenly think of her as a girlfriend. Risa smacks him on the head and tells him to just forget the whole thing ever happened. He follows Risa back to where Nobu and Nakao are, and sees that she is completely shattered by the rejection. Later on, Risa tells him that she can't suddenly stop loving him either and that she will continue to pursue him.
- After returning home from their school trip, Risa falls for their new English teacher, Maity, and proceeds to start the Maity Fan Club. This greatly bothers Ōtani and he tells her that she should close the club and that he doesn't like her being in it, even pointing out that he is the one she really loves. Maity instigates a lot of repressed jealousy over Risa, eventually angering Ōtani to the point of saying some very hurtful things about Risa right in front of her. He hurts himself playing basketball after these events which prompts Risa to take him home on a bike, because despite how he is acting, she still loves him. During this bike ride home, Ōtani tells Risa to not stop loving him and to give him time to figure out how he really feels.
- Ōtani eventually confesses to Risa after a basketball match, but she had fallen asleep right before from staying up all night and didn't hear him. He later gives Risa a bunny necklace on her birthday and confesses to her again with a kiss. Risa somehow misinterprets this and tells her friend that Ōtani isn't her boyfriend which upsets him. He clears this up with Risa later that day saying he would never kiss someone that he didn't consider more than a friend. Risa immediately perks up showing a more loving side of herself which immensely embarrasses Ōtani. Despite this, he is extremely protective over Risa, even going as far as yelling at Seiko for kissing Risa on the cheek and almost starting a fight with an old man on New Years that grabs Risa's arm.
- Seiko Kotobuki (previous): Seiko briefly dated Ōtani after she kissed him for saving her from a dog. They were only briefly together before Ōtani found out Seiko is a transgender woman and broke up with her because he couldn't see passed that. Even so, Ōtani still tells her she is cute and remains her friend.
- Chiharu Tanaka (previous): Chiharu was Ōtani's first (known) high school crush and is the best friend of his now girlfriend, Risa. Ōtani's crush started for Chiharu due to her striking resemble to his ex-girlfriend, Mayu. Chiharu was completely oblivious to Ōtani's feelings for her, and states that she feels he is so easy to talk to because he is short and reminds her of a girl. Ōtani eventually finds out that Chiharu has a crush on his friend, Suzuki, and decides to give them his support instead.
- Mayu Kanzaki (previous): Mayu was Ōtani's first and only girlfriend during junior high. They met through their junior high basketball club where Mayu was the clubs manager. Mayu broke up with Ōtani shortly before they entered high school and immediately started dating a guy that is 198cm (6'5") tall. It is later discovered that she did not break up with Ōtani because he is short, but instead because he ignored her to focus on playing basketball which caused her to develop feelings for someone else that paid more attention to her.
- Heikichi Nakao: Nakao is Ōtani's best friend. They met in their basketball club during their first year of junior high (equivalent to 7th grade) and remained best friends throughout high school and after. Nakao often assists Nobu in picking on Ōtani for anything involving making Risa upset. Ōtani is the only one truly there for Nakao when he becomes distant and depressed over Nobu moving to Hokkaido.
- Nobuko Ishihara: Nobu and Ōtani are not particularly close, but they have known each other since junior high when she started dating his best friend, Nakao. Nobu often picks on Ōtani when he upsets Risa and seems to get a lot of joy out of embarrassing him.
- Ryoji Suzuki: Suzuki and Ōtani met during summer school of their first year of high school (equivalent to 10th grade). Ōtani befriended Suzuki with the intention of setting him up with Risa, but that plan miserably failed. They remained friends regardless.
- Mimi Yoshioka: Mimi is Ōtani's next door neighbor and has been that "annoying little sister" to him since they were young children. Mimi eventually confesses her love to an unsuspecting Ōtani and promptly runs off afterwards. Ōtani later rejects her saying that he simply does not think of her like that, despite this, Mimi does not give up on Ōtani and continues trying to break him and Risa up.
- Shiozaki (塩崎): Shiozaki is a friend of Ōtani's from his university. She refers to Ōtani as "Chappy" because he reminds her of her dog named Chappy. In the brief time that she appeared in final chapter of the original manga, she is shown to enjoy picking on Ōtani. Shiozaki also makes a cameo appearance in Episode 24 of the anime.