TOKYO -- Japan's Naoya Inoue will fight for two world titles in his super-bantamweight debut when he takes on American Stephen Fulton in Yokohama in May, the boxer nicknamed "Monster" said Monday.

The unbeaten Inoue became the first undisputed world bantamweight champion in half a century when he beat England's Paul Butler in December to add the WBO title to his WBC, WBA and IBF belts.

The 29-year-old, who has a 24-0 record with 21 knock-outs, vacated his titles in January to move up to the super-bantamweight division.

He intends to make an instant impact against WBC and WBO title-holder Fulton, who is unbeaten in 21 fights with eight knock-outs.

"All I can do is believe in myself," Inoue told reporters at a press conference in Tokyo.

"When I have gone up a weight class in the past I have done very well in my first fight, so that is a big motivation for me."

Inoue, who has won world titles in three different weight divisions, knocked out Butler in December to become the first undisputed bantamweight world champion since Panama's Enrique Pinder in 1972.

The 28-year-old Fulton is one of two world champions in the super-bantamweight division -- Uzbekistan's Murodjon Akhmadaliev holds the WBA and IBF belts.

Fulton's last fight was a unanimous points decision win over Daniel Roman in June last year.

He called Inoue "a great fighter" in a recorded video message but insisted he had "no concerns at all" about facing him in Japan.

"I like to challenge myself, I like the excitement, so why not take that type of opponent?" said Fulton.

"I feel like I have the style to beat anyone -- I can adjust and do whatever to beat anybody."

© Agence France-Presse