Seiya Maikuma was born on 16 October 1997 in Nagasaki. He came through V-Varen Nagasaki's youth football before joining Cerezo Osaka in January 2022. After developing into one of the J1 League's most reliable right-backs at Cerezo, he moved to Eredivisie side AZ Alkmaar in June 2024.
His AZ career has been productive. The 2024 Eredivisie debut season produced 31 league matches with 2 assists, plus a KNVB Beker appearance. The 2025–26 season has continued at the same level: 6 Eredivisie matches, 2 UEFA Europa Conference League matches, and a KNVB Beker appearance through the first half of the season.
For Japan, Maikuma made his A-team debut in 2024 and has continued to feature in friendly squads.
A 179cm two-footed right-back with elite acceleration, attacking instincts and crossing range, Maikuma is one of Japan's most exciting young right-backs in the Eredivisie. He is in the wider 2026 FIFA World Cup squad picture as a right-back depth option behind Sugawara, Sakai and Yamane.