Arata Kaizaki is the second test subject of the ReLIFE program in Kanto under the watchful eye of Ryo Yoake. Four of them, including Chizuru Hishiro and An Onoya took the ReLIFE drug which makes them physically look 10 years younger.
Pre-ReLIFE- A young adult male with broad shoulders, dark hair and blue eyes.
Post-ReLIFE- His height remained the same, but his frame seemed to have gone away and his face took on much more of an adolescent look. His hair became shorter and his eyes remained the same. Only his appearance changes but not his body.
He likes the act of helping others and caring for everyone. He has a strong sense of justice which is one of his strongest points, but is also a major flaw.
He describes himself as persevering and someone who would stick to something until the end once he has made up his mind.
Little is known about Kaizaki's childhood aside to the fact that he had his life planned out from the beginning. He planned to graduate, have a job, and get married at 25 (which sadly didn't come true, due to his being unable to get a girlfriend and becoming a NEET). His mother covers his living expenses until he was laid off (which eventually became one of the factors that led him to accept the experiment).
He used to work in a company that did a Flower Business under the leadership of his senpai. He was disappointed at the way the people in the company did their work wrongly and blamed it on her. He tried to fight for her sake which did not work as well as he planned. In the end his senior committed suicide, an event which traumatized Kaizaki. Afterwards, he tried to justify her death. which resulted in him being fired from the company, three months after his employment.
The event became a black stain in his life, as well as in his resume which hindered his chances of being employed in other companies, until he eventually turned into a NEET.
Arata is 27 year-old man, unemployed and forced to work odd jobs in order to get by due to his parents cutting him off. His life is changed when he met Ryo Yoake and was offered the chance to better his life. Ryo presented Arata with a card that read ReLIFE which is organization that helps people like him. He tells Arata that he would put through an experiment that'll last a year and if he performs well he might be offered a job at the organization. Excited, Arata takes up the opportunity as Ryo gives him a pill that would make him look like a 17 year old.
Michiru Saiki - Kaizaki's superior at his previous job. She was a victim of constant harassment by her colleagues, something that really bothered him.When Kaizaki tried to help her, the attacks became even worse and Saiki committed suicide. Arata blamed himself for her death and lost faith in society and in his own worth, leading to the events depicted in the story.
Chizuru Hishiro - He becomes her first friend. He thinks she's cute and is impressed she's trying her best to overcome difficulties in her life, unlike him. She initially gave him a little sister vibe, but in the recent chapters he's realized that he's in love with her. However he's unwilling to act, as he sees that playing around with the feelings of a young girl is unhealthy, as the memories will be erased at the end of a year. Kaizaki believes that is a very cruel and unethical thing to do. Currently he supports her as they go through the year keeping his feelings intact. In chapter 197, he said "I love you Hishiro-san, I am completely in love with you".
Rena Kariu - She lends him a pencil on his first day of school. He goes out of his way to help mend her relationship with Honoka and improve the relationship between her and Hishiro. He also was responsible for Ohga realizing his feelings for Kariu. Kariu became more friendly with him on the course of the series although she still insults him due to his exam retakes
Kazuomi Ohga -Ohga was one of the few students to first interact with Kaizaki. Ohga helps Kaizaki prepare for his makeup tests after he fails them. Kaizaki is disappointed at the fact that Ohga is dense even though he is so handsome. Kaizaki makes him realize his love for Kariu and is responsible for him confessing to her. After getting together with Kariu, Ohga had a difficult time deciding universities which led him to consider enrolling to a university outside Aoba which led to more misunderstanding to Kariu as he did not spoke with her about his plans, there is also a tension within his home which sprouted from his parents' separation and his brother becoming a shut in and a NEET. Ohga was able to recover his relationships from both Kariu and his brother and deciding to enter Aoba University instead of an outside university from the advise given by both Kaizaki and Hishiro who came to his rescue.
An Onoya - An was his first adviser in the RELIFE experiment. She had been introduce to be his co - retaker in the exams and had been coerced by Yoake Ryo to seduce him which turned out to be a joke. In the final term of the year and Ohga finally gone out with Kariu, both of them started teasing Kaizaki due to his feelings for Hishiro that he desperately keep under wraps. She,in the shadows desperately want the two of them to be with each other.
- "There is no right answer for getting along. Different people require different answers."
- "Well, you don't have to rush things. You'll make friends in time. I'm sure."
- "Trying to knock others down a peg means lowering yourself. Don't go trampling all the hardwork and trust you've built up. It insults the effort you put in. The only way that would make you happy is if you were a loser who'd giving up on trying."
- "Please, let that iron guard down for a minute. It's only hurting you. I know when you"ve hit rock bottom, people trying to cheer you up can be really annoying. "What would you know?""Just leave me alone." But what if someone you're pushing away is really worried about you? That'd be a shame.
- “Thanks for thinking of me that way. That alone… makes me think this ReLife was worth living. Though you’ll forget me…”
- (About his feelings for Hishiro)"At that moment when I let her go, I wanted to keep holding her and listen to what she was going to say. Why? Why does she have to be a high school student? If only we could have met under different circumstances. If only we can be together from now on. If only she didn't have to forget me---"