He was "very interested in plants and fruit, and surprised to learn how the 20th-century pear had suddenly appeared", but eventually abandoned plans to study botany because his mother favored him to be a physician.

[4] Kawasaki conducted his medical internship year in Chiba and decided to specialize in pediatrics, due to his fondness for children.

[5] After 10 years of researching milk allergy and unusual host-parasite cases, he saw a 4-year-old boy presenting with a myriad of clinical signs he later termed "mucocutaneous lymph node syndrome" (MCLS) in 1961.

[3][8] The paper included comprehensive hand-drawn diagrams of each patient's rashes and has been described as "one of the most beautiful examples of descriptive clinical writing".

[10] In 1970, the Ministry of Health and Welfare established a research committee on MCLS headed by Dr. Fumio Kosaki.

Obituaries paying tribute to Kawasaki were published in medical journals worldwide in the aftermath of his death.