When Naomi Osaka announced herself on tour at 16-years-old by beating Sam Stosur in Stanford, she called it only the "second best" win of her life.
"First being when I first beat my sister," she told *Sports Illustrated* at the time.
Mari Osaka, currently the world No. 326, is the older sibling by two years, and therefore was the dominant sparring partner when they were growing up. And it turns out that dynamic shaped the sisters' tennis experience and taught them both lessons along the way, Mari shared in an open letter for Glamour, **titled "To My Sister Naomi Osaka, a Love Letter."