[7] She first got public attention when she managed to defeat high school and even university students much older than her in her first ever All Japan Table Tennis Championships.

[8] She was also nicknamed Ai-Chan II, a comparison to fellow athlete Ai Fukuhara, who also started playing table tennis at a young age.

Her talent for table tennis was due partly to her parents, both former players, who gave Ishikawa special training since she was young.

She reached the semi-finals of the Women's Singles at the London 2012 Olympics but lost out to eventual gold medal winner; Li Xiaoxia of China.

At the Women's Team Event semi-finals, Kasumi Ishikawa helped Japan to overcome Singapore by defeating her quarter-finals opponent in the Single's, Wang Yuegu in three straight games.

The wins together with Ai Fukuhara overcoming Feng Tianwei in the first game brought Japan to their first table tennis finals in the Olympics in three straight matches.

[13] She also represented Japan in the women's singles event, where she crashed out of the tournament after suffering a cramp in her leg, losing 4–3 to North Korea's Kim Song-i in their third-round match.

[14] At the 2017 World Table Tennis Championships held in Düsseldorf, partnering compatriot Maharu Yoshimura in the mixed doubles event, Ishikawa and Yoshimura progressed through to the final, beating the combination of Fang Bo and Petrissa Solja in the semi-finals, and overcame the Taiwanese pair of Chen Chien-an and Cheng I-ching 4–3 to win the first title in this tournament.

[15] In January 2020, she was announced to be part of the women's table tennis team for the 2020 Tokyo Olympics, together with Ito Mima and Miu Hirano.

[16] Ishikawa defeated Miyuu Kihara in the semi-finals[17] and Mima Ito in the finals to win the All Japan National Championships in 2021 for the first time in five years.