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