|Shatotto will regularly cast Fire as an auto-attack, and occasionally use Origins of Fire, a circular AoE centered on you. At around 80% she will create a Summoning Circle that will regularly summon Blizzard Sprites. These sprites are easy to kill with fire spells, but will build up over time if left unchecked, so take out the circle ASAP before mopping up the sprites.
Once the first circle is down, she'll cast Origins of Ice, a circular AoE that leaves a puddle inflicting Frostbite if you walk over it. At around 60% she'll create another summoning circle, this one summoning Summoned Golems. As before, take the circle out first before dealing with the adds and returning to Shatotto.
In this next phase she'll start casting Origins of Thunder, which summons orbs of the same name that will float toward you and inflict damage and paralysis if they get close. Taking these out should be your top priority so a bad paralysis doesn't ruin your rotation.
Finally, at 20% she'll start casting Origins of Flare. This will hit for heavy damage and inflict Suppuration, increasing the damage of subsequent flares. You'll likely be able to survive two. You will not survive a third. All other attacks and mechanics stop, so it's just dummy time as you try to pour out as much DPS as you can within the time allowed.