Sei Muroya was born on 5 April 1994 in Osaka. He came through Tokyo's youth football and won the AFC U23 Asian Cup with Japan in 2015–16. In September 2020 he moved to Hannover 96 in Germany's 2. Bundesliga.
His Hannover career produced consistent 2. Bundesliga output across multiple seasons. The 2022 season brought 31 league matches with 3 goals and an assist; 2023 produced 25 league matches with 2 goals and 3 assists; 2024 produced 27 league matches.
In June 2025 Muroya returned to FC Tokyo. The 2025 J1 season has produced 17 J1 League matches with an assist.
A 176cm two-footed right-back with elite work rate, attacking instincts and the senior leadership of a multi-league international, Muroya is one of Japan's most experienced full-backs. He is a candidate for the wider 2026 FIFA World Cup squad as a right-back depth option.