Known for his lovingly drawn renditions of physics-defying goals on the pages of soccer manga “Captain Tsubasa,” series creator Yoichi Takahashi was unexpectedly forced to play defense last month — in an intellectual property battle with a Singapore-based startup of murky origin.

On June 17, Takahashi took to Twitter in order to denounce plans by Football Metaverse Pte and its partner Mangaverse Foundation to sell a series of non-fungible tokens — which serve as certificates for digital items such as art and music — themed around “Captain Tsubasa,” describing the project as “illegal” and urging fans not to participate.

“All Captain Tsubasa related NFTs issued by FOOTBALL METAVERSE and MANGAVERSE are illegal,” Tsubasa Co., the company established by Takahashi to manage the series, tweeted in both English and Japanese. “Captain Tsubasa fans, we sincerely hope no one gets caught up in this scam.”