When you complete the main game you’ll find the first DLC story is unlocked in the Extras screen. The 2nd and 3rd will unlocked respectively when you finish each one, and that final CG in the LI galleries are in the 2nd story, ‘Til Death.’
Right, but what about the last CG in the "general"/"other" gallery? I have all of the LI ones
This may count as a spoiler, but I believe it's from the Halloween DLC (I got it from doing August's route).
That was it, thank you!