Here is the full list of all 41 MAMIYA achievements.
Unlocked EX
Viewed DoomsDayDreams Ending 16
Viewed DoomsDayDreams Ending 13
Viewed DoomsDayDreams Ending 15
Viewed DoomsDayDreams Ending 5
Viewed DoomsDayDreams Ending 4
Viewed DoomsDayDreams Ending 1
Viewed DoomsDayDreams Ending 2
Viewed DoomsDayDreams Ending 3
Viewed DoomsDayDreams Ending 8
Viewed DoomsDayDreams Ending 7
Viewed DoomsDayDreams Ending 14
Viewed DoomsDayDreams Ending 6
Viewed DoomsDayDreams Ending 12
Viewed DoomsDayDreams Ending 9
Viewed DoomsDayDreams Ending 10
Viewed DoomsDayDreams Ending 11
Suffered an unfortunate fate in the DoomsDayDreams prologue
Unlocked DoomsDayDreams
Set the True Course for the story
Finished DownFall - Ni'igaki route
Finished DownFall - Arisugawa route
Finished DownFall - Touma route
Took the offered hand
Finished DownFall - Chapter 5
Finished DownFall - Samejima route
Connected with Suou
Truly connected with Haruki
Got rejected by MAMIYA
Truly connected with Ryou
Truly connected with Minato
Focused on the looks
Appreciated beautiful singing
Unlocked DownFall
Finished FallDown - Keito Suou Route
Finished FallDown - Morichika Haruki Route
Finished FallDown - Toujou Minato Route
Finished FallDown - Kikuchi Ryou Route
Unlocked all achievements in MAMIYA
Viewed all Gacha Scenarios
Unlocked all CGs in gallery