|Family||Saki Arima (Mother, deceased)|
Takahiko Arima (Father)
Hiroko Seto (Guardian)
|Occupation||Pianist / Student|
|Japanese Voice||Natsuki Hanae|
|English Voice||Max Mittelman|
Kousei is a piano player and was the youngest pianist ever to win the Saki Competition. However, he quit playing after the death of his mother. His mother's death resulted in his inability to hear the pieces he plays. Following the death of his mother, he lived for two years without playing the piano and saw the world in monotone. But this changes after meeting Kaori Miyazono, a young violinist who pushes Kousei to his limits in an attempt to get his fingers back onto the piano keys.
Kousei is a boy of average height with short black hair. He has dark blue eyes and usually wears his full-framed rectangular black glasses. Kousei is most commonly seen wearing his school uniform, but is also seen wearing casual clothes as well. Although he looks a bit lethargic when he wears glasses, he is very handsome when shown to not be wearing glasses while jumping off from The Bridge of Courage.
As a child, Kousei was calm and obedient. When he is not hanging out with Watari and Tsubaki, Kousei spends most of his day alone in his thoughts. This dense characteristic makes him oblivious to what is going on around him. For instance, he does not notice the rivalry and resentment his fellow piano competitors had for him nor Tsubaki's crush on him. He also stares at Kaori for long, thinking how great of a person she is, which she misinterprets as him having perverted thoughts of her.
Kousei admires Kaori because she is his opposite; he wishes to become more free-spirited like her. The closer Kousei and Kaori get, the more his feelings for her deepen and the more he opens up to other people. She helps him build his confidence and convinces him to perform again.
Kousei's ability was honed through the training of his mother which led to his achieving of technical perfection at a very young age.
Kousei became a piano player at the encouragement of his mother's friend, Hiroko Seto, after Kousei recreated an improvised song that Hiroko was playing towards her husband. This led to his mother becoming his piano mentor and teaching him how to play.
Following a collapse in his mother's health, Kousei's style of learning to play the piano was drastically changed, As a result, Kousei started becoming distant from his friends and focused solely on perfecting his piano skills in an attempt to satisfy his mother and make her happy.
Though Kousei had never met Kaori before, Kaori had always admired him since she first saw him perform. Kaori took up playing the violin hoping to perform with Kousei one day. Throughout the series, they had many adventures in which Kousei slowly gained feelings for Kaori. Each adventure had Kousei realize the importance of himself as a musician, as well as learn more about Kaori and become closer to her, something which eventually flourished into romantic feelings - however, Kousei refused to confess as he was mislead to believe that Kaori was in love with Watari (Kaori's 'Lie in April'). When Kaori collapsed on the day of the Gala Performance due to the sudden paralysis of her legs and received a concussion, Kousei started to doubt himself, seeing his Mom, Saki Arima, in Kaori as both of them has made a huge impact in Kousei's life, and forced him to play the piano. Kousei started to give up on music once again as he felt that music was the one who took away everything that was precious to him. However, after talking to Kaori about not giving up hope at the hospital, Kousei was touched by her words and decided to persevere once more in his last piano competition while Kaori was undergoing surgery. Unfortunately, Kaori was unable to pull through the surgery which led to her death, with her presumably dying on the operating table. Kousei received a letter from Kaori's parents which was written by Kaori before she underwent surgery. In the letter, Kaori expressed her love and gratitude towards Kousei and thanked him for bringing joy and meaning to her life. At the end Kaori wrote that she was in love with Kousei and not Watari (Something which clearly shocked him).
Kousei and Tsubaki have been friends since the day they were born, playing together and growing up incredibly close, being best friends as well as next door neighbours (With Tsubaki calling him her 'hopeless little kid brother'). They go to the same middle school and are usually seen walking home together. Tsubaki at first denies that she likes Kousei, but after various stages of denial, she starts to secretly develop feelings and a crush towards him. She later on confesses to him indirectly about her feelings for him, something which Kousei (being the dense man he is) does not realise the meaning of. On the last episode of the anime, she was shown to be kicking Kousei, stating that she will not leave him alone and will follow him around like his guardian angel.
Kousei and Watari have been friends since they grew up and played together a lot when they were kids. They go to the same junior high school and Watari is one of the few friends that Kousei can trust. Watari constantly gives advice to Kousei, backing him up when Kousei was feeling down. Watari was supposedly Kaori's love and constantly acts lovey-dovey with her which causes Kousei to be jealous. When Kousei tells Watari that he is in love with Kaori, he gives an advice on how to get her to like him and gives Kousei the confidence he needs to visit the ill violinist.
Despite being cheeky and devilish towards Kousei on occasion, she respected him as their friendship grow as they are hanging out more with each other and is encouraged by Kousei to learn a piece. Kousei acted as her tutor and Nagi agreed to take lessons from him every week and worked hard. It is later indirectly seen that Nagi has a crush on Kousei.
Hiroko was the first one to find out that Kousei had perfect pitch and was a genius with the piano at a young age. Saki interpreted this and decided to immediately give Kousei lessons and make him a world class pianist in her place. Later though, it is shown in her own flashback that she blamed herself for Kousei's suffering, saying that if she hadn't told Saki to turn Kousei into a pianist, he wouldn't suffer. Because of this, she decided that she couldn't meddle with Kousei's life anymore.
Emi was amazed and even cried at Kousei on his performance and decided to learn the piano. She grew up to be close with Kousei and Takeshi as they were always competing in piano competitions. They have a mutual relationship but she and Takeshi are angered as Kousei kept winning first place in competitions. It is said that she wanted Kousei to remember his true self.
Kousei has a similiar relationship with Takeshi to Emi with similiar reasons. Takeshi respected Kousei and named him his 'hero' but insisted that he was always a step behind Kousei, which angered Takeshi. This made him frustrated and resulted in him practicing intensely every day, quitting soccer in order to practice and focus on playing piano, and later on, became a great pianist.
- (To Tsubaki) "There's no one who'd ever fall in love with me."
- (To Kaori) "You exist inside spring."
- (To Kaori) "You're in love with food, you're in love with the violin, you're in love with music."
- (To himself) "If you can't hear the sound, then imagine it."
- (To himself) "She moves me with such power like the pounding of my heart."
- (To Saki, as a child) "All I wanted was to make you happy. Even when I wanted to play with Tsubaki and Watari, or when you hit me, I always put up with it and kept practicing. All I wanted was for you to get better! All I wanted was for you to be happy! And yet...I wish you would just die." 
- (To Nagi) "Music might just transcend words." 
- (To himself) "The spring where I met you. A spring...without you."
- (To Kaori) "I had you." 
- (To Kaori) "I want to see you."
- (To Watari) "I... really like Miyazono." 
- (To Hiroko) "I want to see that sight again with my own eyes one more time. That's what made me think...That I'd like to become a really weird pianist!"
- (To himself) "I knew all along. The ghost of my mother was a shadow of my own creation. An excuse for me to run away. My own weakness. Mom isn't there anymore. Mom... is inside me."
- (To Emi and Takeshi) "I have to play. Gotta play. 'Cause I... I made a promise."
- ↑ In early episodes of the anime series, Kousei is mentioned to have brown eyes, though this differs from his physical character design.
- ↑ Anime: Episode 09: Resonance
- ↑ Anime: Episode 17: Twilight
- ↑ Anime: Episode 22: Spring Wind
- ↑ Anime: Episode 11: Light of Life
- ↑ Anime: Episode 20: Hand in Hand