Chasing Jill Achievement
Read a letter left behind by Jill.
This achievement is unlocked by simply finding and collecting a note that has been placed in the gun shop in either of Leon's campaign scenarios. It is found on the counter and upon collecting it, the achievement unlocks.
You can load a save that you may already have near this point in the game and make your way there to collect it, however if you don't you will need to begin a new game to reach this point. If you play on Assisted difficulty, you could speedrun through the game and reach this point in well under an hour to collect it if you are familiar with the game or are otherwise following a walkthrough.