TOKYO, June 10 -- Most corporate separations this week are about retreat. Asics announced one on Wednesday that is about the opposite problem: a brand growing so fast, at margins so fat, that the parent decided the kindest thing was to get out of its way.

The Japanese sportswear maker will spin off Onitsuka Tiger, the nearly 80-year-old fashion sneaker line, into OT Group, a wholly owned subsidiary, through a company split effective January 1, Bloomberg reported, a structure that requires no regulatory approval. Asics framed the move as a way to speed decision-making and sharpen the brand's global competitiveness. Its shares rose nearly 2 percent in Tokyo against a falling broader market, which is how investors say they suspect a listing...