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