Kazuki Takahashi, 60, whose real first name was Kazuo, was discovered wearing snorkelling gear and floating in the sea near Nago, in the southern island prefecture of Okinawa, early on Wednesday and identified a day later, the NHK public broadcaster reported.

According to the Associated Press, the coast guard and the fire department went by boat and watercraft and found the body face down and wearing a snorkelling mask.

A coast guard official said he might have been dead “a day or two”, and the body showed signs of being attacked by a marine creature, possibly sharks.

But the cause of death was still under investigation, the official said, speaking on condition of anonymity as their job does not allow them to be named.

“Yu-Gi-Oh!,” which means “King of Games”, debuted as a serialised comic and ran from 1996 to 2004. It features a boy who solves conflicts using various games.

It led to other series of manga, as well as video games and television series. The official card game went on sale in 1999 and became a worldwide hit.

There was an outpouring of mourning on social media, with US actor Eric Stuart, who did the animation voiceover, posting on Twitter: “An amazingly talented man. Sensei created a role that would help define my voice acting career.”

Fans around the world posted their cards and manga images online, with some pointing out that “Yu-Gi-Oh” had led them to grow interested in Japan. Some recalled how the card game had helped them make their earliest friends.

“We are deeply grateful for the wonderful ‘Yu-Gi-Oh!’ universe that he has created, and our thoughts are with his family and friends at this difficult time,” the London-based YuGiOhNews account said on Twitter and on its official site.