After finishing elementary school, he attends junior high and continues swimming hard. Even after Rin's letters stopped coming, Sosuke continues training in order to, one day, swim at the same level as Rin. In time, his hard work pays off as there is nobody who can beat him in butterfly. However, he begins sensing that something is wrong with his shoulder. When he hears from Gou that Rin has returned to Japan, he works to repair his shoulder before meeting him by going to physical therapy every day. By then, his teammates have surprassed him and Sosuke has decided to quit swimming, believing his dream will never come true. However, seeing Rin's response to swimming relay with Haruka, Makoto Tachibana and Nagisa Hazuki revitalizes his desire to swim with Rin once more.
After transferring to Samezuka Academy, he eventually joins their swimming club. Ever protective of Rin, Sosuke admonishes his friend to forget about friendship and to focus only on his Olympic dream, but Rin replies that he needs his friends to succeed. Sosuke then asks to be "one of those friends" and to be on Samezuka's relay team beside Rin. Rin agrees, changing the rules of relay team selection to allow those who had the greatest desire to swim relay to be on the team versus those with the fastest times.
Sosuke's shoulder injury eventually sidelines him from competitive swimming but following successful surgery, he tells Rin he plans to return. Meanwhile, he continues to train while working and attending school.