Here is the full list of all 25 Head AS Code achievements.
Get your first ending.
Get the minimum amount of endings needed to access the True End.
Get the True End.
Get all endings.
Get the True End with the fewest endings possible.
Unlock your first lock.
Unlock all four locks.
Finish all endings, choices and Active Searches on the blue line.
Finish all endings, choices and Active Searches on the cyan line.
Finish all endings, choices and Active Searches on the green line.
Finish all endings, choices and Active Searches on the lime line.
Finish all endings, choices and Active Searches on the orange line.
Finish all endings, choices and Active Searches on the pink line.
Finish all endings, choices and Active Searches on the purple line.
Finish all endings, choices and Active Searches on the red line.
Finish all endings, choices and Active Searches on the aqua line.
Finish all endings, choices and Active Searches on the yellow line.
Finish all Active Searches.
Unlock all CG art pieces.
Unlock all Lexicon entries.
Read all Lexicon entries. Yes, go back and read them. They're fun.
Check the map during any Active Search.
Witness the change in the game's logo after reaching one ending.
Read a segment that changed after an ending.
Get all achievements.