Kosei Tanaka won world titles in four weight classes in a highly productive career.

On Wednesday, the Japanese fighter announced on social media that he had retired.

"I am retiring as a professional boxer. 11 years of professional life," he wrote on X.

"Thank you so much for all the support over this long period. The reason is entirely due to repeated eye injuries."

Tanaka, who turns 30, on June 15, was a successful amateur, winning four national high school titles, he reached the quarter-finals at the Youth World Championships in 2012 and claimed a silver medal at the ASBC Asian Confederation Youth Boxing Championships in 2013.

Later that year, aged 18, after going 46-5 (13 knockouts), he embarked on his professional career.

In just his fourth fight, 11-months after his debut, he beat Ryuji Hara (TKO 10) to claim the OPBF strawweight title. In his next outing, he won the vacant WBO 105-pound title beating Julian Yedras (UD 12).

After one defense, Tanaka jumped up to junior flyweight where he claimed the vacant WBO 108-pound title, impressively stopping Moises Fuentes (TKO 5).

Tanaka made two defenses before he deemed it time to move up in weight again.

He became a three-weight world champion, doing so in his 12th fight, a record he jointly holds with Vasiliy Lomachenko, when he unseated tough compatriot Sho Kimura (MD 12) for the WBO 112-pound crown.

This time he made three successful title defenses, notably beating former Ring/ unified junior flyweight beltholder Ryoichi Taguchi (UD 12) and future 108-pound kingpin Jonathan Gonzalez (TKO 7).

He attempted to become a four-weight world but fell short against the outstanding WBO junior bantamweight champion Kazuto Ioka (TKO 8). The all-action fighter took off a year before returning and notching four wins to get back into the title picture.

That opportunity came when Junto Nakatani vacated the WBO 115-pound title to head up to bantamweight. Tanaka was matched with Christian Bacasegua to fill the vacancy.

Tanaka used all his experience to win a 12-round unanimous decision. The win also saw him eclipse Oscar De La Hoya's previous record for fewest fight to become a four-weight champion, doing so in his 21st professional bout.

Unfortunately, for Tanaka, in his maiden defense he dropped a close decision to unheralded South African Phumelele Cafu (SD 12) in October 2024.

The rigors of battle appear to have caught up with Tanaka, who walks away with a record of (20-2, 11 KOs).

The Ring wishes Tanaka a happy retirement and all the best for his future endeavors.