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