Stroll through Tokyo on a summer day and you’ll see hand-held fans everywhere. But the light-blue one that Eimi Nakayama was holding on a recent afternoon was a more high-tech variety. Outfitted with a small metal plate that runs on the same science behind semiconductors, it uses electrical currents to generate a chill.

The sensation is “kind of like holding a cold drink against your neck,” said Nakayama, 20, a university student. “Maybe because of the plate, the air flow feels a bit cooler, too.”

The product has lately been sweeping through cities in East Asia, where a deadly heat wave this summer has led to canceled baseball games in South Korea and a new meteorological term in Japan: kokushobi, or “cruel heat day.”