Paul Butler was giddy with anticipation watching Naoya Inoue terrorize yet another opponent.

Inoue, the Japanese dynamo, made mincemeat of future Hall of Famer Nonito Donaire on Tuesday, stopping the Filipino veteran in two rounds of their 12-round, 118-pound title unification bout at Saitama Super Arena in Saitama, Japan.

The win gave Inoue, who was already in possession of the IBF and WBA titles, the WBC belt held by Donaire.

Butler, the WBO champion, holds the last belt in the division. The British boxer was overly impressed by the Japanese champion’s performance, calling Inoue’s latest performance “frightening.” But that did not stop the 33-year-old Ellesmere Port native from shying away from issuing a challenge to perhaps the hardest punching fighter south of 120 pounds the sport has seen in a generation or two.

“Watching as a fan, and not as a potential opponent, you’ve got to respect him,” Butler told IFL TV. “You've got to sit there and admire what he does. He’s frightening in what he does, mate. I honestly thought it would go past seven rounds before he gets him to the body…but wow. Just wow.”

Inoue dropped Donaire once apiece in rounds one and two, before referee Michael Griffin stopped their fight at 1-24 of the second round.

After the bout, Inoue (23-0, 20 KOs) declared his interest in becoming the undisputed champion at 118. Butler reciprocated.

“Yeah, 100 percent,” Butler said of fighting. “Listen, the point of this sport is to become a world champion. When you achieve your goal, you set yourself another goal. Mine is to unify the division, become undisputed.

“That’s a very small minority of boxers that get to win a world title, not many even get to box for the undisputed. I’d be daft not to take that one, mate, absolutely daft. He’s arguably one or two, pound-for-pound great, and he’s absolutely huge in Japan, so why not?”

Butler (34-2, 15 KOs) defeated Jonas Sultan by unanimous decision to win the interim version of the WBO bantamweight title. Butler was subsequently elevated to full champion after the sanctioning body decided to strip his original opponent, John Riel Casimero, for failing to observe certain protocol.

Butler understands, however, that Inoue is a different kettle of fish.

“He’s a complete fighter,” Butler said of Inoue. “He’s one of the best I’ve seen in 20 or 30 years. But listen, you’ve got to test yourself against the best sometimes. I’ll look back on my career and say I won two world titles and I got in there with Inoue, I challenged myself with the best. If I win I win, or if I lose I lose, I can walk away from the sport.”