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