OUTERPLANE Skyward Tower Hard Floor 15 Clear Guide

To clear Skyward Tower Hard Floor 15 in OUTERPLANE, eliminate the supporting minions first, control the boss's Action Gauge with speed debuffs and buffs, and time your Weakness Gauge depletion to shatter the boss right before their ultimate attack fires. Relying on an uncoordinated damage race fails because the boss gains aggressive Action Gauge acceleration, high defensive resilience outside of Break states, and wipe-inducing multi-target skills.

Recommended Team Composition

A consistent clear requires a balanced four-hero squad built around single-target burst, Action Gauge manipulation, debuff cleansing, and buff stripping.

Role	Viable Units	Stage Function
Single-Target Finisher	Noa, Ame, Rin	Conserves Action Points (AP) to unleash Level 2 or 3 Burst skills and execute Chain Finisher strikes during Break.
Action Gauge & Turn Buffer	Valentine, Tamara	Grants partywide Critical Chance buffs and boosts allied turn meter to act before enemy shields go up.
Debuffer & Stripper	Eternal, Dolly	Strips enemy barriers and offensive buffs while applying Defense Down and Speed Down.
Cleanser & Healer	Tio, Saeran, Mene	Cleanses incoming debuffs, provides sustained healing, and prevents party members from falling to burst spikes.

Tio is particularly effective as the sustain anchor on this floor. Her passive ability triggers free cleanses and emergency healing whenever an ally is debuffed, preserving your Action Points for offensive setups.

Weakness Gauge and Chain Attack Timing

The boss possesses a segmented Weakness Gauge that drastically reduces incoming damage while intact. Allowing the boss to cast an ultimate while this gauge is full typically wipes the team.

Pool Chain Points (CP) and AP: Build CP through basic attacks and dual attacks during normal turns. Avoid spending AP on intermediate burst levels before the boss is vulnerable.
Monitor the Boss's Special Meter: Track how fast the boss accumulates their ultimate attack charge. Do not dump high-depletion skills while the boss's gauge is far from full.
Trigger the Break State Intentionally: When the boss is one or two gauge hits away from breaking—and right before their ultimate charges fully—launch your four-hero Chain Attack.
Execute During Break: Shaking the final gauge segment triggers an immediate Break, canceling the queued boss ultimate. Set your primary Attacker or Striker in the final Chain slot as the Finisher, then spend banked AP on Level 2 or Level 3 Burst skills while Defense Down is active.

Stage Battle Sequence

Follow this turn order to prevent the enemy formation from overwhelming your defenses:

Turn 1 (Setup): Open with your Action Gauge buffer (Valentine or Tamara) to push allied turn meters and apply teamwide Critical Chance buffs. Apply Speed Down or Defense Down to the frontline.
Minion Cleanup: Direct all single-target burst toward the auxiliary minions immediately. Removing them eliminates extraneous incoming damage, cleans up disruptive debuffs, and ensures later dual attacks redirect entirely onto the boss.
Pacing the Boss: Once the minions are down, chip the boss while managing team health. Save multi-hit abilities to lower the Weakness Gauge as the boss approaches their ultimate.
Break Phase Execution: Trigger your Chain Attack to cancel the boss's ultimate, exploit the Break damage multiplier with your primary Finisher, and reset your positioning.
Post-Break Recovery: After the boss recovers from Break, top off party health with your healer, reapply Speed Down, and cycle basic skills to regenerate CP for the next Break loop.

Gear Benchmarks and Troubleshooting

If your runs fail, adjust your gear and targeting based on these failure points:

Failure Symptom	Cause	Solution
Squad wipes early	Sustain unit is too slow to react	Equip Speed sets on your cleanser to guarantee they take a turn before enemy follow-ups land.
Defense Down fails to land	Insufficient debuffer Effectiveness	Raise debuffer Effectiveness to at least 60% on units like Eternal or Dolly to bypass boss Resistance.
Boss casts ultimate through attacks	Weakness Gauge depletion mistimed	Hold multi-hit abilities and Chain Attacks until the boss's special gauge is nearly full.
Low damage during Break	AP exhausted prior to Break	Use basic attacks during non-Break phases to save AP exclusively for Burst 2 and 3 skills.

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Emily Johnson

Emily writes practical mobile strategy guides with a focus on resource planning, base progression, and the early decisions that shape a long-term account.