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