In Days Past are little retrospectives by Chizuru about some of the events that occured with characters other than the main ones. They are pretty interesting, and give some insight in to the lives of the other characters.
I really enjoyed them, and they gave insight in to some situations through out the game. Obviously, if you haven't played any of the main routes, there will be spoilers in these side stories. If you'd like to watch the main story first, there are links below.
Hakuōki: Stories of the Shinsengumi is a Visual Novel for the PS3. Don't expect FPS or Action/Adventure game elements. This is a visual novel game, so if you don't enjoy good story, and lots of reading, this might not be for you. There will be no commentary, just the game play, and story.