Buddleja curviflora Hook. et Arn. f. venenifera (Makino) T.Yamaz.

Family: Scrophulariaceae
Japanese: ウラジロフジウツギ (裏白藤空木) [Urajiro Fuji Utsugi]

I love the way the shape of the flowers blooming on the curved racemes echos the tapered shape of the leaves. Although it grows wild, I think it's beautiful enough for place in the garden

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）