A 12-month-old girl developed a serious immune system disorder called hemophagocytic lymphohistiocytosis triggered by Epstein-Barr virus infection. Despite aggressive treatment, she developed a life-threatening fungal infection caused by mucormycosis that spread throughout her digestive system. The case illustrates how fungal infections can rapidly progress and become fatal in children with severely weakened immune systems, emphasizing the need for doctors to recognize early warning signs like tissue darkening on the skin.