Asarum kumageanum Masam.

Family: Aristolochiaceae
Japanese: クワイバカンアオイ [Kuwaiba Kan-aoi]

Yakushima is home to (at least) two species of Asarum. The leaves may be solid or varigated. The flowers are hard to find and are often hidden by fallen leaves and twigs. I am not always confident in my identifation.

References:
新版　屋久島の植物 川原勝征,初島住彦(監修),2001：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13日
Prof. Summer's Web Garden 2012: http://www7a.biglobe.ne.jp/~flower_world/