Ranma ½ (1989)

S01E126 The Date-Monster of Watermelon Island

Kuno finds himself stranded on the shore, disoriented and sporting a watermelon atop his head, having lost all memory of who he is. As he navigates the strange landscape of Watermelon Island, he encounters quirky locals and unravels the mystery of his past, all while trying to figure out how he ended up in such a bizarre situation.