Ren first sees Nanami helping a lost little girl find her mother. It was by coincidence that Ren meets her again during the academy's entrance exams. He is surprisingly very fond and affectionate towards Nanami compared to other girls and even gave her the nickname "Little Lamb" and "My Lady." He also gets extremely jealous whenever another guy gets close to her, especially Masato. As the story progressed, Ren opened his heart to his love for music again when Nanami gathered the lyrics he ripped on top of the school roof. He claims that he is in "debt" to Nanami and will do anything to make her happy. Believably, Ren has shown a whole new kind of "affection" towards Nanami, and it's no longer the shallow kind that he usually shows to any girl.
In season 2 episode 6, he tells Haruka that she is a bad girl for making him so crazy about her. He almost kisses her after this, but stops when he sees that she is uncomfortable with it. He said that he will wait for her to grow up a little more before continuing.
He says the same thing in season 3 episode 1, when they run into each other at the lake. Haruka complements his saxophone playing, and he pulls her close telling her that she is more beautiful than both the moon and cherry blossoms. He then says that simply looking at her is enough to rend his heart in two.
In Season 4 Episode one, after STARISH pulls her away from QUARTET NIGHT, Ren hold Haruka in a suggestive pose and says that "nobody else(other than her) lights a fire in him anymore." He later says that he missed the days when she wrote music only for them(STARISH).
Ren first meets Masato at a social gathering back when they were kids. He claimed that the party was boring and invited Masato to play with him at the lake. It was again that they meet each other at Saotome Academy with the same goal in mind. In the early semester, Masato hated Ren with the fact he didn't take his love for music seriously and ended up punching him. It was later on that Masato forgave him and they continued their friendly rivalry. The rivalry further intensified when Masato finds out that Ren also decides to choose Nanami Haruka as his graduation partner. But their rivalry between Haruka did not end after their debut.
As the series continues, Ren's feelings for Haruka, like Masato's, have only just kept growing.
A fellow member of STARISH. Ren calls Ittoki 'Ikki' as a nickname.
A fellow like member of STARISH, Ren's nickname for Tokiya is 'Ichi.' Ren was once a little distrusting of Tokiya, due to the latter keep the secret of him being HAYATO from eveyone. However, once he came clean and showed that he was serious in his desire to sing as a member of STARISH, Ren forgave him.
A fellow member of STARISH. Ren appears to have a good relationship with Natsuki as both a professional and a friend. When his alter ego, Satsuki appears, Ren assists the others in trying to get his glasses back on him to revert him back to Natsuki.
A fellow member of STARISH, Ren likes to tease Syo about his size, but they are friends nonetheless. When they are partnered together for the group project with Cecil, they clashed over their different views on how they thought it should go. However, thanks to Haruka, they were able to blend their ideas perfectly, and made up in the end.
Ren's first interactions with Cecil did not go over well, with him being quite jealous of the new arrival. When he witnessed Cecil kiss Haruka's hand, he grew extremely tense and jealous. Once Cecil tries to actually kiss her, Ren charges up with the rest of STARISH Ina fit of jealous rage, and pulls him off of her. He then shields her from Cecil when he tries to kiss her again.
Once they were put into a unit for a group project with Syo, and they all clashed over which direction they thought it should go. However, Haruka was able to combine all of their ideas flawlessly, and they all made up because of it.