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