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