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