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