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