Here is the full list of all 50 I am Setsuna achievements. It takes around 30-35 hours to unlock all of the achievements on Windows.
Obtained all achievements.
Fluxation occurred 200 times.
Defeated all the Spritnite-Eaten Monsters.
Defeated all members of the Pengy species.
Defeated all members of the Hoot-Hoot species.
Defeated the Ruler of Time.
Defeated the Dark Samsara's final form.
Used one megalixir.
Ate Gaia's Blessings Stew.
Ate Starberry Cake.
Ate Nive Vegetable Stew.
Ate Gatherington Fries.
Listened to all the youth's lines and defeated him.
Met the youth.
Fluxation occurred ten times in Support Spritnite.
Saw the Laniff Ruins.
Obtained the Eclipse spritnite.
Obtained the Dragnarok spritnite.
Added maximum Fluxes to a spritnite stone.
Saw ???.
Obtained the Rebellion spritnite.
Obtained the Genesis spritnite.
Obtained the Doom spritnite.
Obtained the Gearadia spritnite.
Obtained the Holy Light spritnite.
Sailed on the exploratory ship.
Inflicted 1000 damage in a single hit.
Met Eutess.
Saw the Moolbeld Ruins.
Made one monster drop eight materials at once.
Fluxation occurred four times in a single battle.
Met Rhydderch.
Defeated enemies with all Kill types.
Inflicted 500 damage in a single hit.
Used combos in Momentum mode 30 times.
Met Sayagi.
Ate Horse Oak Casserole.
Met Cornelius.
Fluxation occurred ten times in Command Spritnite.
Saw the Apparth Ruins.
Defeated ten enemies with Over Kill.
Met Hydor.
Used Momentum mode 100 times.
Met Akash.
Made one monster drop four materials at once.
Used Momentum mode ten times in a single battle.
Met Freyja.
Defeated ten enemies with Exact Kill.
Met Raishin.
Met Hapsper.