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