The story starts out yuri between 2 childhood friends the main girl is blond, but the 2nd girl gets involved in a relationship with a guy on a train that starts by getting SA'd. Later when the main girl finds out the guy was her brother. Then the brother and sister also starts getting into a relationship through blackmail. The siblings actually got separated when their parents divorced and it lookedlike the siblings were about to do it that time before being caught by the mother.It has 5 parts the last I have seen it. Got too involved in the story.