Thanatos Tower
Floor 3 - Will Cage
Overview
This fight is different from the ones thus far. There are no phases but its full of a few mechanics you need to keep an eye on if you're DPS so you can react accordingly. There are two bosses though their HP pools are shared, they have the same size, race, and element so your gear is the same no matter which one you're focused on.
The major mechanic of this fight is an aura that everyone on the team receives which determines where to stand on the map and if you don't move into that area in time you die. Once the fight begins everyone will be assigned an aura and after a few seconds a wall will go up preventing movement between the two areas and you'll die if you're not on the correct side. Furthermore, you cannot interact with enemies or team members on the other side of this wall unless an aura change happens and the walls temporarily go down.
Therefore it is important that your team have a few healers, two tanks, and perhaps even a few wanderer/minstrels to help with spot heals.
Orbs
Fortunately there are four orbs on that map above circled in green that grant players a buff that allows them to cast over the wall. Therefore, I would strongly advise that you give two to your Royal Guards and Arch Bishops so they can help the other side when things go south.
Once your party grabs all four orbs the fight will begin. You must have four party members to pick up all four orbs otherwise you cannot begin this fight.
Watch Your Aura
When the fight begins those who didn't get an orb you will gain an aura indicated both under your character and on the far right side of the screen next to the boss health bars. This aura is either Purple or Orange and it indicates the color of the ground where you should be standing. When that aura turns on you have just a few seconds to move onto the floor that matches the color of your aura.
This means if you have a purple aura you need to move into the Inner Circle since the ground there is purple, and if you have an orange aura you need to move to the Outer Circle since that ground is orange, simple enough.
A wall will appear between these two zones shortly after the fight begins and no one may pass through it until certain intervals and during the fight when your aura may change and you have to quickly move to the other area before the wall goes up again and you die. If you see the wall go down that's an indicator that a change happened so check to see if your aura changed and move accordingly.
Outer Circle
The group in the outer circle will be fighting the Worry Polymer. Your only real job here is to stay alive and watch for either aura changes or large explosions that happen when a large part of the outer circle turns red.
Inner Circle
The group inside the circle will be fighting the Sorrow Polymer. While fighting the boss it will send out waves that will fear you if hit so stay with the group and watch out for these.
As the fight goes on a mob, the Heart of Sorrow will spawn inside the circle somewhere. This will heal the bosses HP so you want to kill this quickly. When you kill it a countdown will begin in one of the two hibernate timers on the right indicating that an explosion is imminent either on the inner or outer circle.
Explosions
As I mentioned above, killing a Heart of Sorrow starter a timer on one of the two Hibernating indicators. The top indicator is for the inner circle while the bottom one is for the outer circle.
A large part of that portion of that part of the map light up red before the explosion happens so run for your life if you're in it because this will kill you if you're caught by it. Since the Hearts will heal the boss they have to be killed so keep your eyes peeled for explosions, especially if you're part of the outer group since you may not realize a heart just died.
This is the primary reason why you want your Priests and Royal Guards want to have the orbs so they can res those on the other side of the wall that get caught by this since the explosion area is quite large.
Finishing Up
Just burn down the bosses, kill hearts if you're on the inside, and watch for explosions for an easy victory, no phase changes to worry about here.