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