Heloniopsis sp.

Family: Melanthiaceae
Japanese: ツクシショウジョウバカマ (Tsukushi Shoujoubakama) or ヤクシマショウジョウバカマ(Yakushima Shoujobakama)

The Yakushima varient of H. orientalis is similar to the Kirishima variety, but is typically less than 10 cm tall. However, there are exceptions, such as the plant pictured above, which was a good 15 cm tall. I suspect that's why there's descpencies about the species name. There can be multiple flowers on the stem.

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（ 2016年8月21日）.