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