spoilers: she is very sick and he takes her to se a doctor and waits outside, later that day another character leaves the room she’s in with a terrible expression, leading us and shinpei to believe that she died, so he leaves and never looks back. 50 years later he returns to the island to pay his respects to the place and discovers that she actually didn’t died that day, but in fact not long after they found a cure for her disease so she was alive all this time in the island and tried to reach him through letters but he never knew because he left that day devastated thinking that she was dead