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