Hamasaki practiced judo for 8 years, achieving 2nd dan. She stopped practicing judo after finishing college and was working in an office. A year and a half later, Hamasaki began training in MMA around 2008, partly for dieting purposes. She was introduced to the Abe Ani Combat Club by her friend and AACC member Rina Tomita, and although Hamasaki knew about MMA, she was unaware of women's MMA.
Hamasaki made her MMA debut on at Shooto Gig Central Vol. 19, defeating Kinuka Sasaki via submission in the second round. Joining Jewels for the first Lightweight Queen tournament, Hamasaki submitted South Korean kickboxer Han Sol Lee with an Americana in just 48 seconds in the opening round of the tournament at Jewels 9th Ring on. At Jewels 11th Ring on, Hamasaki defeated Sakura Nomura after three competitive rounds via unanimous decision in the Lightweight Queen tournament semi-finals. In the same event, Hamasaki defeated South Korean Seo Hee Ham by unanimous decision, surprising commentators by holding her own in the striking exchanges against the experienced Korean kickboxer. Hamasaki won the tournament in the process and became the first Jewels Lightweight Queen Champion. Hamasaki was scheduled to face Lisa Ellis in a non-title bout at Jewels 12th Ring on in Tokyo, Japan. However, Ellis suffered a calf injury and was forced to withdraw from the fight. Hamasaki was then set to face Jessica Aguilar at 12th Ring instead, but the event was cancelled after the Tōhoku earthquake and tsunami earlier in the day. Hamasaki faced Mizuki Inoue in a non-title bout at Jewels 16th Ring on in Tokyo. She defeated Inoue by unanimous decision. Hamasaki defended her Jewels title in a rematch against Seo Hee Ham at Jewels 17th Ring on. She won the fight by TKO after the first round when Ham could not continue due to injury. Hamasaki faced Yuka Tsuji in a Jewels title fight at Jewels 19th Ring on in Osaka, Japan. She won the fight by submission due to a kimura in the first round. Hamasaki was scheduled to face Jasminka Cive at ' on in Kansas City, Kansas. However, Cive was unable to secure a visa to compete and Hamasaki faced Lacey Schuckman instead. She defeated Schuckman by submission due to an armbar late in the third round. Hamasaki was expected to face Carla Esparza at Invicta FC 4 in January 2013. However, Hamasaki withdrew from the fight in order to defend her Jewels title. She faced Emi Fujino at Jewels 22nd Ring on and defeated Fujino by unanimous decision. Hamasaki agreed to face Carla Esparza for the Invicta FC Strawweight Championship at ' on, but Esparza withdrew due to a knee injury. Hamasaki was then matched up against Cláudia Gadelha. She was defeated by TKO in the third round.
Other activities
Hamasaki participated in a submission grappling mini-tournament held at Jewels 10th Ring on, where she won the tournament by defeating Emi Tomimatsu via armbar submission in the second round and Yuko Oya, also by armbar in the first round. Hamasaki faced Saori Ishioka in a grappling match at Jewels 14th Ring on. She won the match by split decision.
