[1] She won the 2016 Rio Olympic gold medal for Women's 48 kg freestyle wrestling by 3-2 decision over Mariya Stadnik of Azerbaijan.

By the time she entered middle school, she transferred to MIYAHARA GYM run by her father where the members are known to train more intensely.

In September, she proceeded to win favorably at the Wrestling World Championship, and she defeated Venezuelan Mayelis Caripa, avenging herself from her second place finish in the previous tournament.

At the World Championship, she beat Polish Iwona Matkowka by a huge difference with a score of 10 to 2, achieving her second consecutive win.

Tosaka was given two points due to an activity time (AT) warning, but was able to tie the score in the last ten seconds with a one-legged tackle.

With this win, as long as she participated in the Japanese National Championship in December, she would be offered to be a representative at the 2016 Olympics in Rio de Janeiro.

In June, she visit the Toyama Prefecture Office and expressed her determination for the Olympics saying " I want to win the gold metal no matter what".

On August 17 at the Olympics in Rio, she defeated Kazakhstan's Zhuldyz Eshimova in the second round 6 to 0, American Haley Augello 11 to 2 in the quarterfinals, and China’s Sun Yanan 8 to 3 in the semifinals.

In the finals, Azerbaijan's Stadnik had a lead of 2 to 1 until just before the end of the match when Tosaka performed a one-legged tackle, giving her the win at 3 to 2 and earning her the gold medal.

In September, she returned to compete in the National Japanese Women's Open Wrestling Championship after over a year in the 53kg weight class and won.

At the National Japanese Wrestling Championship in December, she competed in the new 50kg weight class, but withdrew after winning the quarterfinals in order to not worsen the injuries on her left knee and ankle.

In June of 2018, she lost 2 to 6 at the National Japanese Invitaional Championship against Irie Yuki from the Japan Self-Defense Force's Physical Training School, placing in third.