Pyrola japonica Klenze ex Alef.

Family: Ericaceae
Japanese: イチヤクソウ (一薬草) [Ichakusō]

I've only come across this once, in a low-altitude mixed forest, although it has the appearance of something that you might find in a flower bed.

References:
Tropicos.org. Missouri Botanical Garden. http://www.tropicos.org/Name/50048775 (13 Oct 2014)
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）