The story revolves around a 27-year-old unemployed man who is given a pill by a researcher, Riou, from the Reality Laboratory. The pill, called the "Rebirth" pill, allows him to become a teenager again and relive his life. The experiment is designed to help people correct their past mistakes, and the protagonist is chosen as a test subject.
As he navigates his new life as a high school student, he meets various characters, including a girl named Reina who is initially hostile towards him but eventually becomes his friend. He also meets Chizuru, a socially awkward but intelligent student who becomes his friend.
However, things become complicated when Reina, who is also a test subject, tries to confess her feelings to the protagonist, but he rejects her. Meanwhile, Riou is monitoring the protagonist's progress and is concerned about the potential consequences of the experiment.
The protagonist eventually falls in love with Reina, and they start dating. However, the experiment is set to last only a year, after which the protagonist's memories of his experiences will be erased. In a surprising twist, it is revealed that Chizuru is also a test subject, and since both she and the protagonist are test subjects, they will not forget their memories of each other. The story ends with the protagonist and Reina declaring their love for each other, and the possibility of a new beginning for them.
Here are the key facts from the text:
1. The story starts with a 27-year-old unemployed and single man who is drunk.
2. The man's mom calls him and tells him she won't give him any more money if he doesn't get his life together.
3. A man named Riou shows up and offers the protagonist a pill that will help him rebuild his life by making him a teenager again.
4. The protagonist takes the pill and becomes a 17-year-old high school student.
5. The experiment lasts for a year, during which time the protagonist's expenses will be paid for.
6. The protagonist must attend high school and pass as a student.
7. The protagonist meets a girl named Chizuru who is a prodigy but socially awkward.
8. Chizuru and the protagonist become friends, along with another girl named Reina.
9. Reina is initially angry and resentful towards the protagonist, but they eventually become friends.
10. The protagonist saves Reina from falling down the stairs, which changes her attitude towards him.
11. Reina has a crush on the protagonist, but he rejects her.
12. Riou is monitoring the protagonist's progress and intervenes when necessary.
13. Han, a 27-year-old woman who also took the pill, is a test subject and is being monitored by Riou.
14. Han tries to seduce the protagonist, but he rejects her.
15. Reina sprains her ankle and is unable to participate in a volleyball tournament.
16. The protagonist tries to console Reina, but she pushes him away.
17. Reina's childhood friends help the protagonist understand her feelings.
18. The protagonist realizes he likes Reina and they start going out together.
19. Chizuru also develops feelings for the protagonist, but doesn't act on them because she's 27 years old.
20. Chizuru is also a subject of the relaxation experiment, but the protagonist doesn't know this.
21. Because both the protagonist and Chizuru are test subjects, they will remember each other after the experiment ends.