Ryuichiro Isaka (井坂 龍一郎, Isaka Ryūichirō) is a supporting character in the Sekai-ichi Hatsukoi series. He is the Senior Managing Director at Marukawa Publishing, and later becomes President.

Isaka is a main character in the series Junjou Mistake, which takes place in the same world as Sekai-ichi Hatsukoi. Part of his story was adapted into one of the anime episodes, and it shows his relationship with Kaoru Asahina.


Isaka has dark brown hair and blue-grey eyes. He has a fair skin tone. He usually wears a suit.


Isaka and Kaoru Asahina are childhood friends. They became playmates after Isaka's father, who owns a famous publishing house named Marukawa Publishing (similar to Ritsu Onodera), decided to take care of Asahina's family when he happened upon Asahina's father attempting to commit a family suicide after the bankruptcy of his company. Isaka admits how he was a brat during his childhood years as a result of his rich upbringing, but that once he saw Asahina's bruised and bandaged appearance had immediately decided to take him under his wing and look out for him.

Asahina has deep gratitude and respect toward Isaka's father for taking care of his family in their time of need. Isaka confuses this respect for romantic affections which leads Isaka to mistakenly think that Asahina is in love with his father. Isaka mentions having been in love with Asahina for a long time starting from when he was a child but felt it was hopeless due to his belief that Asahina was in love with his father. Asahina later reveals to Ryuichiro that he had been in love with him ever since they were children. The specific moment he states this happened was when Ryuichiro gave Asahina a potted plant called the Amadokoro. Amadokoro meaning "cheer up" in the Japanese language of flowers, he gave it to Asahina after seeing his fragile state from the attempted family suicide. He states it was the first time Isaka had seen Asahina smile.

Isaka scouted Akihiko Usami when he was younger after coming across one of his stories on his desk while waiting in his room to give him a book. Isaka himself had always wanted to be a writer but gave up after reading Usami's writing, realising he'd never be able to write something like that and had no real talent as a writer in the first place. He orders Usami to send his work to the Marukawa publishing house. Isaka, who always knew he was naturally very talented at editing books he knows will be successful, finally resolves to 'ride [the] company to the top' devoting himself to be an editor to many top selling authors and books.

In the past, Isaka dealt with gossip about nepotism regardless of the fact that most of his authors were quite obscure before Isaka's editing skills made them hits. He is not ashamed of his family name, which his co-workers believed was the sole reason for his success, but instead embraces it, as he later tells Ritsu to.

Relationships Edit

Kaoru Asahina Edit

They are childhood friends and, in their adult years, lovers. After Asahina's father tried to commit a family suicide when he was a boy, Isaka's father had them take refuge in his home. As a result, Asahina gave an Amadokoro plant (meaning 'cheer' in Japanese) to him and made a personal vow to look out for him. Isaka's plant gift made Asahina smile for the first time in a long while. It is later discovered that Asahina had tended to the plant to where, even 10 years later, it remained healthy and intact. From there on out, both established a strong connection that eventually became romantic love. They grew up together and can often recognize the emotions of the other.

As a young child, Isaka recognised that he was deeply in love with Asahina, but also came to falsely believe that Asahina was in love with his father due to how he always smiled and behaved around him. After a while, this came head to head with a confrontation between the young men. The two clarify that they have always been in love with each other, and what Isaka thought to be romantic love was only Asahina's great admiration and respect for Isaka's father. From here, they consummate their relationship, becoming an official couple. By the time the plots of Sekai-ichi Hatsukoi and Junjou Romantica take place, the two have been together for ten years and, in the anime, celebrate their ten year anniversary. 

Trivia Edit

  • The official name of the history of Asahina and Isaka is Junjou Mistake. They are called that way for several confusions in their relationship. Sometimes this couple is called "Junjou Mystique". 
  • He usually calls Ritsu "Nanahikari" (that is someone who is under the influence of his father).



Sekai-ichi Hatsukoi characters
Character icon Ritsu
Character icon Takano
Character icon Chiaki
Character icon Hatori
Character icon Kisa
Character icon Yukina
Character icon Yokozawa
Character icon Kirishima
Masamune Takano Chiaki Yoshino Yoshiyuki Hatori Shouta
Takafumi Yokozawa Zen

Marukawa employees Kanade MinoRyuichiro IsakaKaoru AsahinaSasakiKazuma HenmiYasuda GouSanae HoshinoHasegawaTinkle
Mangaka Yuu YanaseYukina MutouNanako SaitouErika IchinoseIori SatouKaitou
Friends and family SaekiAn KohinataChinatsu YoshinoYoriko YoshinoRio KojimaNao KiyomiyaHiyori KirishimaRitsu's motherSorata
Other Arata HaitaniKeiki TezukaKensuke SaigusaTakuya KusagawaRyouichi SumiAkihiko UsamiKisa's one-night-stand


  1. Stated by Kaoru Asahina.