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