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