Syzygium jambos (L.) Alston

Family: Myrtaceae
English: Rose Apple
Japanese: フトモモ (蒲桃) [Futomomo] or ホトウ [Hotō]

According to [九州野山の花], this is a small naturalized tree. It blooms and bears edible fruit that seem to be somewhere between a green pepper and a peach. For a good read, see https://www.hort.purdue.edu/newcrop/morton/rose_apple.html .

References:
九州野山の花 片野田逸朗,2004：南方新社
米倉浩司・梶田忠 (2003-)　「BG Plants 和名－学名インデックス」（YList），http://ylist.info（ 2019年8月14日）
Morton, J. 1987. Rose Apple. p. 383–386. In: Fruits of warm climates. Julia F. Morton, Miami, FL. via NewCROP, Center for New Crops & Pants Products, Purdue University. Retrieved September 4, 2016 from https://www.hort.purdue.edu/newcrop/morton/rose_apple.html