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