Yamashita becomes Japan's first woman pro referee
Yamashita, 36, was named in May alongside France's Stephanie Frappart and Rwanda's Salima Mukansanga as officials for Qatar later this year -- the first women to referee at a men's World Cup.
Yamashita has now signed a professional contract with the Japan Football Association and spent her first day on the job giving a talk to school children.
Her new role comes less than a year after Japan launched its first professional women's football league, the WE League.
Yamashita, the first woman to take charge of a men's Asian Champions League match, said she thought it was "good to turn the attention on women".
"The goal is to get to the point where it's not a big deal that a woman is refereeing a men's match, but at this stage I'm happy this is making a splash," she said.
Yamashita, Frappart and Mukansanga were chosen among 36 referees for the World Cup in November-December, with a further three women named on the list of 69 assistants for the first time.
Yamashita said she was looking forward to "breathing the World Cup air" in Qatar and was trying to speed up her decision-making.
"That's something you can always improve on, whichever game you're refereeing," she said.
"Even if the action is happening at a dizzying pace, if you can increase your decision-making speed, you can make each decision clearly."
Yamashita, who became the first woman to officiate a game in Japan's domestic J-League last year, explained the job of a referee to children and answered their questions at the JFA's headquarters on Monday.
"I was nervous throughout -- when I got my cards out, my hands were trembling," she said afterwards.
"I was nervous but really happy to see their eyes sparkling as they listened intently. I had a lot of fun."