JAPANESE superstar and unified (WBA, WBC, IBF) bantamweight champion Naoya "The Monster" Inoue is all set to return to the ring on December 13 and barring last-minute changes his likely opponent will be WBO counterpart Paul Butler of the United Kingdom.

Winning the WBO crown will complete Inoue's mission of becoming the first Asian boxer to become undisputed champion in the four-belt (WBC, WBA, IBF and WBO) era.

For the record, there have been only eight undisputed champs in the four-belt era: Bernard Hopkins (middleweight, 2004), Jermain Taylor (middleweight, 2005), Terence Crawford (junior welterweight, 2017), Oleksandr Usyk (cruiserweight, 2018), Josh Taylor (junior welterweight, 2021), Saul "Canelo" Alvarez (super middleweight, 2021), Jermell Charlo (junior middleweight, 2022) and Devin Haney (lightweight, 2022).

The quest to be part of the prestigious list is the reason why Inoue is extending his stay in the bantamweight or 118-pound division. Truth be told, Inoue has cleaned up the division and he could have easily moved up to junior featherweight (122 lbs) following his second round knockout of Nonito Donaire Jr. on June 7.

Inoue, 23-0 with 20 knockouts, is heavily-favored to beat Butler, a fleet-footed boxer who was only promoted to WBO bantamweight champion after Filipino John Riel Casimero was stripped of the title in April.

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If only Casimero stayed the course, he would have been Inoue's opponent this December.

Inoue and Casimero were originally scheduled to fight in April 2020 for the WBA, IBF and WBO bantamweight crowns. Casimero was coming off a stunning knockout win over Zolani Tete in November 2019 for the WBO diadem and was looked upon as a legitimate threat to then WBA-IBF champ Inoue.

Alas, the fight was called off when the sporting world went on lockdown mode due to the Covid-19 pandemic. When pro boxing activities resumed in the United States sometime in June 2020, the boxers went their separate ways. Casimero bamboozled a hapless George Micah in September 2020 while Inoue stopped Jason Moloney a month later.

Casimero was still in a position to secure a fight with Inoue. The Filipino WBO champ booked a December 11, 2021 title defense against Butler in Dubai. A victory by Casimero would have allowed him to retain the WBO title and stay in line for a unification fight with Inoue. Unfortunately, Casimero pulled out of the Butler fight due to viral gastritis.

The WBO allowed Casimero to keep the title and the fight with Butler was reset to April 2022 in Liverpool. The fight hit another snag when the British Boxing Board of Control (BBBofC) refused to sanction it after Casimero allegedly violated its medical guidelines. Casimero was caught using the sauna days before the fight and the BBBofC claimed this violated its guidelines. The BBBofC prohibits the use of sauna to drastically cut weight.

Fed up with Casimero's shenanigans, the WBO stripped the Filipino of the title and sanctioned a fight between Butler and Filipino Jonas Sultan for the interim WBO bantamweight on April 22. Butler outboxed Sultan in 12 rounds for the interim crown. A few weeks after Casimero was stripped of the WBO crown, Butler was promoted to full-fledged WBO bantamweight champ.

As can be deduced, Butler secured the WBO crown via the backdoor. Casimero was heavily favored to beat Butler but his infractions resulted in him losing the WBO crown even before he could throw a punch at the Englishman. Butler ended up benefiting from Casimero's ill-advised moves.

The WBO title was the only reason Inoue was interested in fighting Casimero. With the WBO title now with Butler, Inoue's attention predictably shifted to the Englishman. Casimero talked tough and challenged Inoue to fight him on several occasions, but Inoue did not take the bait knowing fully well that he stands to gain nothing in a fight with John Riel.

Butler successfully bumped off Casimero from Inoue's radar. Butler also showed no interest in fighting Casimero because he stands to earn more in a unification fight with Inoue. Butler called Casimero "horrible, childish" after their fight was called off again.

Casimero has been relegated to the backseat. Inoue has hinted that the fight with Butler will be his last at bantamweight. Inoue is already plotting to move up to the junior featherweight division and fight WBC-WBO champ Stephen Fulton of the United States.

Fulton is 21-0 with 8 knockouts. He does not have the paralyzing power of Inoue, but the WBC-WBO junior featherweight champ has a clear size advantage and boxing skills that can befuddle the Japanese.

Inoue has his ring plans all figured out. In the meantime, there is still no word on when Casimero will emerge from his cocoon. Casimero last fought on Aug. 14, 2021, beating Guillermo Rigondeaux.