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