The Level 70 trial Castrum Fluminis, also known as Tsukuyomi NM, can be unlocked by accepting the Level 70 MSQ “The Primary Agreement” from Hien in Kienkan (X:6.1, Y:6.0). This quest is part of the patch 4.3 Main Scenario Questline for the Stormblood expansion.
This guide will cover all of the battle mechanics for every phase of the trial.
Unlocking Quest: The Primary Agreement
You can begin unlocking Castrum Fluminis by accepting the Level 70 MSQ “The Primary Agreement.” This MSQ is locked behind the patch 4.3 storyline of the Stormblood expansion, so you’ll need to finish every MSQ leading up to that point, including every MSQ from the previous expansion.
Once that’s all set, talk to Hien in Kienkan (X:6.1, Y:6.0) to begin.
In this quest, Hien is preparing for a prisoner swap with the Garlean empire.
After talking to Doma’s prince, head to Glittering Basin in Yanxia (X:26.2, Y:36.4) and speak with the Confederate Skipper to travel to the meeting place.
Upon talking to the Confederate Skipper, a long cutscene will appear.
Watch it in its entirety to see how the prisoner swap unfolded as well as Yotsuyu’s transformation into the primal Tsukuyomi.
After doing that, Castrum Fluminis will be unlocked.
This trial requires at least a Level 70 Disciple of War or Magic job and an average item level of 335 to enter.
Trial Boss: Tsukuyomi
Castrum Fluminis can be safely soloed with a high-level tank character with updated gear.
Do note that you’ll still need to do “Selenomancy” correctly and you must have enough DPS to defeat the Specter mobs in Phase 2 to survive. However, if you’re doing this trial for the first time, you’ll likely do it through the Duty Finder.
Read about the boss’ mechanics below so you can smoothly clear the trial.
Phase 1: Nightfall and Midnight Haze
Torment Unto Death > Zashiki-asobi > Nightfall (Steel of the Underworld) > Reprimand > Midnight Haze > Nightfall (Lead of the Underworld) > Nightbloom.
- Torment Unto Death: The boss will mark her primary target for a non-telegraphed frontal cleave tankbuster. Face the boss away from the party at all times.
- Zashiki-asobi: Fans will drop around the arena in a set pattern and explode into large circle AoEs. The first AoE will always appear in the center, followed by more AoEs appearing clockwise around the arena. Run to where the last fan will drop, wait for the center AoE to go off, then run back to the center.
- Nightfall: The boss will draw one of its weapons and use its corresponding attacks. In later phases, the weapon drawn through “Nightfall” will be randomized.
- Steel of the Underworld (Sword): A large frontal cone AoE that applies a stacking “Vulnerability Up” debuff for 60 seconds.
- Lead of the Underworld (Gun): A line stack-up marker on a random player. Stand inside the marker to share incoming damage.
- Reprimand: A room-wide AoE attack. Shield and heal through the damage.
- Midnight Haze: Two “Midnight Haze” mobs will tether and slowly float toward one another. If both mobs meet, they’ll use “To Ashes,” a room-wide AoE attack that applies a stacking “Damage Down” debuff for 30 seconds. Killing one haze will cause the remaining haze to cast “To Ashes.”
- Nightbloom (Phase 1): Another room-wide AoE attack that stuns the party with “Down for the Count” for 16 seconds and signals the start of Phase 2.
Phase 2: Specter Mobs and Nightbloom
Specter of the Matriarch + Specter of the Patriarch > Specter of the Homeland x3 + Specter of the Empire x3 > Specter of Asahi > Concentrativity > Specter of Zenos > Nightbloom.
- Specter Mobs: Throughout the phase, Specter mobs will attack Yotsuyu. Each attack will add an extra point to the “Suffering” gauge that’s already constantly increasing. If the gauge reaches 100, your party will wipe. Kill the Specter mobs as soon as possible.
- Concentrativity (Specter of Zenos): When the “Specter of Zenos” first appears, it’ll use a room-wide AoE knockback attack and stun everyone with “Down for the Count” for 10 seconds.
- Nightbloom (Phase 2): A room-wide AoE attack that deals damage based on the “Suffering” gauge. If the gauge reaches 100, “Nightbloom” will deal 500,000 damage. Defeat all the Specter mobs as soon as possible.
Phase 3: Selenomancy
Selenomancy > Lunar Halo + Nightfall > Antitwilight > Torment Unto Death > Zashiki-asobi > Nightfall > Torment Unto Death > Selenomancy > Midnight Haze > Lunar Halo + Nightfall > Perilune > Dance of the Dead.
- Selenomancy: The boss will split the arena into black and white. Then, you’ll receive one of two stacking statuses: “Moonlit” or “Moonshadowed,” indicated by a marker on top of your head.
Standing on either side will increase your stack every few seconds with its corresponding status. If you reach five stacks with either status, you’ll receive a 4-second “Doom” debuff and a 15-second “Bleeding” DoT.
To handle the Selenomancy mechanic, run to the opposite-colored section of your current status once you reach three stacks to refresh your status.
A good indicator to switch is when your marker changes into a half-eclipse.
- Lunar Halo: Two orbs will spawn large donut AoEs during “Selenomancy.” Make sure you refresh your status while dodging the donut AoEs.
- Antitwilight or Perilune: A room-wide AoE attack that dispels “Moonlit” and “Moonshadowed” and transforms the arena back to normal.
- Dance of the Dead: A room-wide AoE attack that signals the start of Phase 4.
Phase 4: Lunacy and Dark/Bright Blade
Lunacy > Bright/Dark Blade > Reprimand > Bright/Dark Blade > Zashiki-asobi + Lunacy > Reprimand > Torment Unto Death > Zashiki-asobi + Reprimand > Repeat from the first Bright/Dark Blade.
- Lunacy: A three-hit stack marker on a random player. Stand inside the marker for all three hits to mitigate incoming damage.
- Bright Blade: A 200-degree AoE attack from the boss’ left side that applies a stacking “Vulnerability Up” debuff for 60 seconds.
- Dark Blade: A 200-degree AoE attack from the boss’ right side that also applies a stacking “Vulnerability Up” debuff for 60 seconds.
- Tsukuyomi Triple Triad Card (not guaranteed)