According to Akitashoten, the voice cast of OVA "Aki-Sora" was changed. The reason for the change was not announced. The OVA is about incest taboo between a brother and a sister and will be released on December 18th.
and why is this described as ecchi? there is actually no ecchi in the manga, no panty shots or random nudity, they just end up fuckin each other, and I never seen an ecchi anime where u cum on your sisters tits. >.>