In 2003 the Japanese chain Mister Donut put a new shape in its case: a ring of eight small balls that pull apart one at a time. It called it the Pon de Ring, after Brazilian pão de queijo, and made it with tapioca flour. The result was chewy where a donut is soft.
Hawaii got there by another road. In 1992 Charmaine Ocasek fried mashed taro and sweet rice flour into poi mochi. The two ideas met in Honolulu bakeries, and the ring shape followed Hawaiian bakers to the mainland.
Then it went everywhere at once. The biggest chain, Mochinut, opened in Cerritos, California in March 2020 and had 148 shops three years later, pairing mochi donuts with Korean corn dogs. Independents picked up the format and ran with it: Korean American sisters in Phoenix, a Thai restaurateur in Colorado Springs, a community college student in Cedar Rapids. Most of them are gluten-free without trying to be, because rice flour is the whole point.