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