Kaidou Ren (海棠 零; Kaidou Ren) is one of the two main characters in the "Super Lovers" manga and anime written by Abe Miyuki. Ren is the youngest of the Kaidou brothers and met Haruko in an orphanage while taking her dogs for a walk. Exactly what happened in his past remains unknown.
When he was first adopted Ren had long hair, but Haruko cut it with a razor in the bathroom. When Haru learned of this, it became clear to him why Ren disliked bathrooms so much.
Ren didn't care what kind of clothes he was wearing or if he was wearing any at all. Haru and Haruko both noticed that there were marks left from cigarette burns on the soles of his feet. They assumed firstly that it may have happened while he was with his birth parents, or because of the orphanage. Knowing that Ren was always without shoes while playing outside in the Canadian mountains, most wouldn't have acknowledged them from the inevitable scars and bruises.
He is said to also be shorter than the common for his age, which infuriates him when he is reminded or made to feel small by other means, as connotations of being called cute or Haru's references to him being a child.
Ren's clothes are hand-me-downs from Aki.
Ren is a very straightforward individual who is always honest with his feelings. He usually never hides what he is feeling and most of the time tells the truth, rarely ever lying. In the manga, Ren keeps his promise of concealing Natsuo's identity and lies to Haru.
Ren keeps a fairly expressionless face, but can show emotions like any other person. He abnormally becomes more obedient when he gets mad at Haru.
Ren was found when he was six, lying on the road. Even though he was found in Canada, Ren could speak Japanese fluently. When they found him, he only remembered his name and age.
Haruko met Ren three months before Haru arrived in Canada when Ren was almost eight years old. She originally didn't plan on adopting any children, but adopted Ren because while passing by the orphanage one day, her dogs "loved that brat".
After that, Haruko tried her best to find something about Ren's past, but it was almost impossible.
It was shown later (during Haruko's visit to Japan), that Haruko had the lawyer Mikiko do a background check on a woman from a hospital in Seattle. She was in her twenties with Asian descent. This woman who died from drug over-dose, spoke to a nurse about selling her own child. She lived not too far from where Ren was found. Due to the influence of drugs, she was very vague but mentioned her child being named Ren or Allen. Unfortunately the motel that the woman stayed at had no traces of a child living there and the woman died shortly afterwards. Three months after her death, Ren was found in a town called Save (East of Vancouver) and 30km away from Seattle. In theory, Ren's mother was a drug addict who sold her son for more drugs which later killed her, but there is not enough evidence to prove this. (Vol 3, Ch 10)
Ren is hardworking, honest, straightforward, and trustworthy. He supposedly doesn't remember anything from his past other than his name and age. He was found when he was six years old on the road and taken into an orphanage for almost two years until he was adopted by Haruko. It is implied that Ren was abused while he was at the orphanage, but he doesn't talk about it.While he was in Canada, he usually spent his mornings playing with the dogs at the river, and then going elsewhere with them later. When Ren brought Haru a lunch box full of berries, Haru pointed out that Ren was covered in mud as usual. The berries probably grew near the playground frequented by Ren.
Ren is an emotional mess as is made clear throughout the progression of the manga. He has "under-developed" emotions, from Haru's point of view, and so lacks the complexity of Haru's which confuses and even scares him. This makes Ren hesitant in allowing Haru to show affection from the offset of their relationship, flinching at affectionate hugs, forehead kisses and his friendly, caring demeanour. Also, his lacking emotions prevent simple social acting, as he can't fake smile as he doesn't know how; further emphasising his lack of a normal upbringing as the cause of his lapses in normal personality and awareness of his age. This, coupled with his different culture from Canada, makes him stand out further, as he lacks the same level of Japanese linguistics at his educational level and etiquette to "authority figures" as his PE teacher/'hometeacher' criticises.
Haruko said that at first Ren would only say "food" and "sleep". He rarely talked, but when he did, it felt like interesting matters described through the eyes of a child. Ren never had any childish demands. He even slept outside, with his dogs, and he would only eat sparingly, often returning with a full meal that he'd been given while he plays outside. Ren is shown to dislike crowded areas, generally preferring the country-side and being slightly withdrawn from societal values.
Because of Haru, Ren began to wear shoes and clothes, take baths, eat properly and at the table, sleep comfortably in the house (especially in Haru's arms) and communicate his feelings when he's hungry, when something hurts, manners, western etiquette, etc.
When Ren lost his lunch box in the river, Haru realised he liked rice very much. Ren dislikes when he's called "a child" and "short" or anything implying he's immature and young, such as affectionately being dubbed "cute".
In Tokyo, Ren wasn't used to Japanese culture. He spent most of the time at the library, studying Chinese and Japanese classics. When Ren wanted to buy some manga, Haru thought that Ren ""can look his age'"'  too sometimes."
After being adopted by Haruko, Ren was finally able to meet his new older brother, Haru. Their first encounter didn't go well, but after a few days, Ren was surprised to see Haru getting along so well with the dogs. Unlike Haru, Ren needed a month to deal with Lepton and Quark, but Haru said:
"They're special, because they're my 'brothers'. Those three are new faces, but Quark and Lepton were born when I was still here. We grew up together like brothers would've. Do you get it? " — Haru
The more Haru learnt about Ren's past the more he understood him and was able to deal with him better, much to Ren's anxiety. When Ren was kissed by Haru for the first time, on the forehead, Ren thought to himself:
"Don't get close to him. He's definitely a scary human being. " — Ren
Even if he called Haru "a scary human being", Ren began to listen to Haru's words and was surprised when he realized that Haru was going to return to Japan soon. When Ren asked Haru about this, Haru replied he still had half of the summer vacation left, also that he and Ren still hadn't gone fishing together, nor played with the fireworks. Ren was so touched that he began crying.
"I'm scared of nice people. That's why, of all the people I met, Haru is definitely, definitely, the scariest." — Ren
When Haru was sick, he made Ren promise that he'd come to Japan too to live together there. Ren told him that he'd think about it, but Haru turned that into a promise. After the accident, Haru didn't remember Ren anymore, but after five years, Ren kept his promise and came to Japan, much to Haru's surprise as he had no memories of his last trip to Canada.
Before they passed away, Haru's father and his wife had adopted Ren. Ren was now the fourth son of the Kaidou family and Haru's third and youngest brother.
Ren's adopted older brother and guardian
Without realising it himself, Ren began to listen to Haru and became close to him in less than a week. Both of them feel that they can rest better whenever the other is close. When he arrived in Japan for the first time, Ren told Aki and Shima that Haru was all the family he needed. Haru tends to be over-affectionate to Ren, which can annoy him as he is happy at receiving attention but also dislikes being treated as a child. Haru also enjoys kissing him even on the lips, something that surprises Ren at first. By chapter 9, he realised that he saw Haru in a romantic view and confessed to him. The two become closer over the series. Ren occasionally tries to have sex with Haru, but he's interrupted by the twins or other unlucky bystander like in chapters 9, 11, and 18. Haru also helped Ren masturbate in chapters 9 and 15. By chapter 18, the two seem to be officially together.
Ren's adopted twin brothers
At first, it was a bit difficult for Ren to deal with the twins. Even if Shima was more understanding, Aki was the one who told Ren he'd never accept him as a younger brother, but the moment Ren was in danger, Aki helped Ren immediately, without a second thought, even scolding Haru for leaving Ren home alone. He has a much more friendly relationship with Shima, compared to Aki, and discusses how Haru taught him many things over their time in Canada together. Such as; holding cutlery, how to bathe, wear clothes, etc, and even how to sleep in a bed (having previously slept in the garage with the dogs, deduced by Haru as being because he was simply not used to it).
Ren's foster mother
Ren sees Haruko as 'the boss' and a very kind person. Also, even if Haruko couldn't spend much time with Ren due to her deadlines, it seems like she'd immediately worry and search for him if something happened to Ren.
Ren's best friend
He first appeared in chapter 5. Ever since the two are almost always seen hanging out together at school. Ren thinks Juuzen has strange speech and behavior, but thinks he's a nice guy too. Juuzen is aware of Ren's feelings and knows about his romantic relationship with Haru, but doesn't get bothered by it. He treats Ren like a normal guy friend. He enjoys Ren's honesty, observant nature, and subtle kindness but gets annoyed when Ren talks about being sexually repressed. He also tried to defend Ren from bullies. Ren in turn enjoys his company and confides in him.
Ren's best female friend
One of the few women he interacts with in the series. They both attended the same middle school and became quick friends. Ren has stated she is the only female classmate he feels comfortable around and Kiri in turn enjoys hanging out with Ren. He has even come over to her house to help train her family's new dog.