This game is the sequel of Kindred [Subject 6244], it's twice longer with 6 endings instead of 4, it's basically the same thing but more opened with more choices.
You need to do the 4 endings of the first game, and then try to aim for the 6 endings of this one if you want the entire story.
It's a good little visual novel and yeah now I'm kinda waiting for the third Kindred game which is to be released next October