Some brands strive to win favor with fashionistas; others cultivate credibility among sports enthusiasts. And then there’s Nike—the company that established its name among athletes now hosts runway shows, collaborates with top designers, and is the most-mentioned fashion brand on Instagram. It’s invested years of research in creating a new sports bra, a woven-yarn running shoe, and a soccer cleat that rises above the ankle. Now, it’s turning up the focus on the female market