Re-Main follows Minato, a young man who awakens from a coma with amnesia, having lost all memory of his middle school years, a period when he was a star water polo player.
He initially wants to distance himself from the sport, realizing how far he's fallen from his former skill.
However, fate, in the form of his new high school and a long-forgotten promise, draws him back to water polo.
Despite his lack of confidence and need to relearn the fundamentals, Minato joins the school's struggling water polo club.
The club must recruit enough members to even field a team, while Minato strives to rediscover his lost talent and passion for the game, aiming to become a top player once more.