Common name: Bugleweed
This is the kiran-sou(sou means grass in Japanese). A close match from Days of Plants by Ciaobou Hany. シソ科 キランソウ属 Ajuga decumbens. They are native to Honshu and Kyushu island in Japan and can also be found on the mainland continent China.
They range from 5 – 15 cm in height, are mounding and spread quickly. Itdoes well in shady and damp areas.
See another species at this page.