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