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