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