If you just want to unlock all the scenes, go into the .ini file in the game directory, and add these lines, underneath the
[LonaRPG_Rec] tag:
Once unlocked, Scenes can be viewed (replayed) by visiting the Fortune Teller (2 Map Tiles north of the Noer Tavern) and speaking with the fortune teller.
Achievements can be similarly unlocked by finding their section in the .ini file and changing values, but I don't have them all unlocked, and even if I did, they serve as good markers for tracking progress and other things to do in the game, so I wouldn't recommend overriding them in general. There's no gameplay or CG locked behind achievement progress.