Koi Kaze, Kuro to Kin no Akanai Kagi. Recommendations
Kuro to Kin no Akanai Kagi and Koi Kaze have in common:
~love story between brother and sister
~both are mature and should not be watched by people under 17 years
While Kuro to Kin no Akanai Kagi is adapted in 2 OVA's of 29min(the story might go too fast or have plot holes), Koi Kaze's story is explored wider, in 13 episodes (24min).
Difference is that Kuro to Kin no Akanai Kagi is a reverse harem and Koi Kaze is seinen.