Return to 1967, My Classmate Is Named Sadako

[Non-fantasy, light novel, original fantasy, suspense and supernatural, daily love] When he woke up, Kaito Inoue found that he had traveled to Japan in 1967 and became an ordinary college student. After joining the university's drama club, he activated a strange golden finger called the [Causal Interference System]. The first and only long-term mission released by the system is to prevent his new classmate, Sadako Yamamura, from reaching a destined tragic ending. By increasing Sadako's "happiness index", you can get various rewards. But if her "desperation value" increases, extremely terrifying supernatural events will happen around Inoue Kaito. For his own life, and for the sake of this taciturn, talented but isolated girl, Inoue Kaito decided that he would reverse this destined tragedy! "Classmate, have you ever heard of...'Live with a smile'?"