As an allmate, Ren takes the appearance of a small dark blue Japanese Spitz dog. He has dark eyes that compliment his fur, and is always seen with his tongue sticking out. Ren wears a collar with silver studs and a small syringe charm that Nine had given Aoba hooked at the center of it. He is often called a "bundle of blue fur" due to his fluffy coat. Ren is one of the older allmate models and is always seen with Aoba, constantly monitoring his health and safety.
During Rhyme battles, he takes on the appearance of a young man, due to his avatar settings. He sports dark blue hair reminiscent of his fur, a headdress that covers his eyes, and a large dark blue cape covering most of his body down to his knees. He wears light grey pants with a black belt and blue boots that look similar to his cape. He is tall and has a very pale complexion. Without his cape, he is shown to be very muscular and has multiple black tattoos that range from the sides of his face to his shoulder blades and down his arms. His ears are slightly pointed and they each bear a large ring. He also has "tender amber eyes" as described by Aoba and bears sharp canine teeth.
In Ren's good ending in both the first game and in DRAMAtical Murder Re:connect, Ren takes up the appearance of Sei. However, he begins to resemble a younger version of his Rhyme appearance rather than Sei, which was something he mentioned would happen as his consciousness became permanently implemented into Sei's body.
In Ren's bad ending, due to the mechanical virus spreading through his system, combined with the anger and despair over the belief that Aoba has never really loved him and never will, Ren's appearance becomes highly animalistic. His canine teeth turn into large fangs and his eyes glow with rage. His tattoos also begin to spread over his body, resembling fur, and his fingers become sharp and claw-like. Much like Koujaku in his bad end, Ren becomes so animalistic that he loses the ability to properly speak, and instead growls and snarls.
Ren's most notable feature is his surprisingly deep and masculine voice, deeper than even Usui's, despite taking the form of a small, cute dog a majority of the time.
Ren is shown to be very mature among allmates (like Tori), and even humans as well, to an extent. He is very passive in most conversations, usually taking things literally and misunderstanding certain sayings, leaving Aoba to explain things to him. He maintains a calm demeanor throughout the entire game, even during fights, except for when Aoba is in sudden danger.
Despite his laid-back attitude, he is deeply conflicted about his feelings for Aoba, and his duty to keep him in check. Ren is also very caring about those around him. He and Beni share a casual friendship, due to Aoba and Koujaku's relationship, and he converses with Tori a few times. When Aoba confides in Ren about the men in his life (in their respective routes), Ren usually talks about them with understanding and neutrality, in order to help Aoba with his relationships.
As Ren becomes more and more human in Re:connect, he begins to smile and even laugh on occasion. He begins to experience emotions more clearly now that he's an independent physical being, rather than an Allmate or simply a part of Aoba. He becomes flustered and embarrassed easily, especially around Aoba, due to the fact that he still maintains many of his dog-like habits from when he was an allmate (holding things in his mouth, smelling unfamiliar objects, etc.).
KoujakuRen has a good relationship with Koujaku. Ren will often comment on Koujaku's personality. When Aoba becomes distraught in Flame Willow, he admits that Koujaku can be troublesome and irresponsible when it comes to women. Koujaku seems to be one of the few people Ren allows to hold him, implying that Ren places great trust into him, as he doesn't seem to like being fondled or held by most of the other characters (especially Clear).Ren also has a very good relationship with Koujaku's allmate, Beni. Beni is usually shown asking for Ren when Koujaku and Aoba meet up, and Ren usually allows Beni to rest in sleep mode on his fur coat.
Noiz finds Ren interesting because he is an older model, and Aoba is still using him. Noiz threatened Aoba with his ability to easily take Ren away from him, but he seemed to have been bluffing, as the most he ever does is perform maintenance on Ren after he received critical damage and a virus during a drive-by. Much to Aoba's surprise, Noiz saves Ren from being completely overwritten by the bug.
Noiz and Ren do not interact very much outside of the games. During the April Fool's Special, however, he trotted up to Noiz and Mink (who were sitting next to each other) and sprawled out across their legs to prevent them from leaving, amusing the others. Ren politely asked both men to be careful and not drop him, and Mink and Noiz, surprisingly, don't move and make sure to be careful of him.
Mink and Ren have a very strained relationship at first. When Aoba asks Ren why Mink is the way he is, Ren simply responds that it's just Mink's personality, and says that Aoba shouldn't let it bother him too much. Mink seems to have little to no regard for Ren's well-being, and says that Allmates are "just goods" when ordering Aoba to install a USB chip into Ren. However, this does not seem to bother Ren as he actually does place trust in Mink, and he's convinced that if Mink has a plan, it is guaranteed to succeed one hundred percent.
In Mink's Re:connect good end, Ren helps Aoba track down Mink in his home country by helping him translate around town. During Aoba and Mink's reuniting, Ren is very supportive of Aoba and keeps a look out for him. It's implied both he and Mink warm up to each other, since they are now living together. Ren and Tori also share a bond, Tori usually referring to Ren as "the blue one" and asking how he was doing when they met each other again.
Mink and Ren do not interact very much outside of the games. During the April Fool's Special, however, he trotted up to Noiz and Mink (who were sitting next to each other) and sprawled out across their legs to prevent them from leaving, amusing the others. Ren politely asked both men to be careful and not drop him, and Mink and Noiz, surprisingly, don't move and make sure to be careful of him.
When they first interacted, Clear asks Ren why he does not refer to Aoba as "Master", since he is below him, to which Ren says that Aoba treats him as his equal. Due to both parties being robots, they share similar qualities, such as their social status regarding humans and their usefulness to them, and concerns.
In Clear's Re:connect good end, Clear is ecstatic to see Ren again, holding him and fluffing up his fur in the process, much to Ren's dismay. Ren was happy to see Clear again as well, but he offered to stay behind instead of seeing where Clear used to live, as Tae might have been worried if no one was there when she returned home.
Like Aoba, Ren is very protective of Tae. He looks out for her, and tries to make sure she doesn't need to worry about Aoba. When he reunited with her in Sei's body, during his Re:connect good end, Tae was taken aback, but softly welcomed both him and Sei back home.
Sei was aware of both Ren and the other Aoba (Desire) being separated from Aoba's consciousness, but also recognized that Ren had become an individual existence, thanks to Aoba accepting his feelings for him. He asked Ren to protect Aoba from then on, and after Oval Tower collapsed, Sei transferred Ren's consciousness into his own body, giving him his own physical being in reality. This was Sei's final present for Aoba, and he wished for them to happy together.
- A running gag in the games is Ren's charm, which attracts many of the characters. For example, his appearance alone causes many to talk about how adorable and fluffy he is, and desire to hold him. It seems to even work on stoic characters like Mink and Noiz, to an extent (see Relationships).
- During the bad ends of each character (except his own), in which Aoba fails Scrap, Ren's fate is left unknown. He is not shown nor referred to in any of them. The only one that mentions his status at all is Virus and Trip's ending, in which he was left "unconscious", and it's implied he is left behind in Platinum Jail, broken forever.
- Ren's height in Sei's body is 175cm, a few centimeters taller than Aoba.
- Ren's bloodtype in his human body is A.
Yoshie • Kou • Hagima • Yuzawa • Takemoto • Theo • Haruka • Nine • Takahashi