Touma Tachibana begins his journey as a middle school student before advancing to Meisei High School. His early life was shaped by loss and new beginnings: his biological mother, Naoko Tachibana, a noted ace softball pitcher and national tournament runner-up, passed away when he was three. At age six, his father Eisuke Tachibana remarried Mayumi Sawai, forming a blended family with her children, Soichiro and Otomi.

Naturally friendly and outgoing, Touma easily attracts people. He shares the exact birthday as his stepbrother Soichiro, born ten minutes later. Their childhood featured a baseball rivalry; Touma ultimately became the pitcher due to his superior speed and a decisive game of rock-paper-scissors, forging their pitcher-catcher battery dynamic. His bond with his stepsister Otomi is profound. As his first and most devoted fan, she overcame childhood shyness through their connection. Touma performs best with her support, though he dislikes her nickname for him, "Tou-chan."

His baseball path faced obstacles. During middle school at Meisei, coach preference initially sidelined him in favor of Daisuke Nikaidou for the ace position. This resolved by his final year, allowing him to claim the ace role, a status he maintained as Meisei High's first-year ace pitcher. This athletic lineage connects to Meisei's past, where both his biological father Eisuke and Soichiro's late father Keiichi Sawai—Meisei's former ace pitcher before a career-ending injury—once played.

Personal tragedy struck when Eisuke died unexpectedly from a heart attack during a crucial game for Meisei's national tournament hopes. This loss deeply affected Touma, causing emotional distress and physical symptoms like arm weakness during games. As the last surviving member of his biological family, he navigates a complex path marked by familial bonds, athletic pressure, and the enduring impact of grief.