On December 20, 2010 Yon was found to be curled up and unmoving near a dried stream. He was brought into the center's rehabilitation room, where it was discovered that he had pulmonary edema, which had nearly killed him; however, he was able to eat by the next day and gradually got better. He was unable to walk for the remainder of December, though by the end of January he had regained this ability and, during February and March, he improved enough to be able to walk up and down stairs. However, his condition then took a turn for the worse, and he died on the night of April 9 at an estimated fifteen years and one month old. He weighed 3.5 kilograms and was 78.5 centimeters long. He is the oldest Iriomote cat on record.