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