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