He’s been friends with a boy named Nishikori since elementary school, and they both took the same tennis classes. Back then, he was the most talented, but by the time they entered High School, their positions reversed as Nishikori became the ace of the tennis club and was popular with girls, which caused him to feel jealous and start avoiding his friend. However one day, they scheduled to meet for a morning practice, but he stood his friend up, although he came to regret it and intended to apologize to him the following day, but he got into an accident while riding on his bike that claimed his life. His spirit lingered however, hoping to apologize to his friend. Matsugo appeared at his funeral to guide him, but decided to coach him on how to restore his friendship instead. Under the tutorship of “Friendship Master”, he was taught to hold Nishikori’s right shoulder as a basic friendship pose, which is bothersome to Nishikori while playing tennis, and to hinder any pictures of him with a girl by leaving a ghostly hand in front, for Matsugo considers women to be annoyances.
Rinne was sought by Nishikori, and both he and Sakura see Matsuoka and then Matsugo, and upon learning his lingering attachment, all it took to restore his friendship with Nishikori was just to make him visible so he can apologize for standing him up, which allows him to pass on then.