I won't call this manga incest because of 2 things. First, they aren't blood related. Even the MC is not his father biological son. Second, Akira keeps her last name, she still loves her real dad so much she doesn't want to change. So unless they say the are step-sibling, no one knows.
I'm... very disappointed. Sasha could have been a great character. It's like we took a wrong turn and step in to corrupted universe somewhere along the way. After checking out the artist doujin, I think he's planned this to happen for a long time.