Ryo Miyaichi was born on 14 December 1992 in Okazaki, Aichi. He moved to England at 18 to join Arsenal in 2011, with subsequent loan spells at Bolton, FC Twente and FC St. Pauli. Despite his early promise, recurring injuries cut short his Arsenal years. With Arsenal he was part of the squad that won the FA Cup in 2013–14.
After permanent moves to FC St. Pauli in 2015, he joined Yokohama F. Marinos in summer 2021. With F. Marinos he won the J1 League in 2022, the Super Cup in 2023, and the EAFF E-1 Football Championship with Japan in 2022.
The 2023 season produced 18 J1 matches with 2 goals; 2024 brought 32 J1 matches with 2 goals and 3 assists, plus 7 AFC Champions League Elite matches; 2025 has produced 22 J1 League matches.
A 181cm two-footed left-sided attacker with elite acceleration and the senior leadership of an early-pioneer Japanese export, Miyaichi is one of Japan's most respected veteran attackers. He is in the wider 2026 FIFA World Cup squad picture as a senior wide attacking option.