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