We present the case of a 3-month-old male infant patient who initially presented with severe dehydration with acute kidney injury secondary to COVID-19. Regarding the individual's previous history, the patient had congenital heart disease and was taking furosemide and captopril. The patient improved after initial hydration therapy. However, on the fourth day of hospitalization, the patient suddenly deteriorated and was found to have MIS-C. The patient's clinical course progressively worsened despite maximum support, and he died from severe MIS-C. We conclude that during the COVID-19 period, MIS-C is a serious health problem that should be considered in the differential diagnosis of patients with acute kidney injury.