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