Tokyo Stock Exchange

Traders Chasing Pokemon Dream Now Battle Over Nintendo's Value

After investors pushed up Nintendo Co. shares with a fervor only matched by gamers chasing Pikachu, traders are now locking horns over how much the high-flying stock is worth.

Bears have boosted short interest in Nintendo to its highest in five months after the stock doubled in just over a week. The other camp includes Yasuo Sakuma of Bayview Asset Management Co., who says the rally has long-term potential as the mobile app Pokemon Go is rolled out to more countries and the gamemaker expands its location-mapping technology to the rest of its lineup, including Super Mario Brothers and Zelda.

"The way the stock has risen is abnormal," says Sakuma, Tokyo-based chief...