Eternal Waltz Arc in NTE - How to Get Fadia's Signature S-Rank

The Eternal Waltz is an S-Rank Synthesis Arc in Neverness to Everness and Fadia's signature weapon. It boosts Max HP by 20% at base and adds a 10-second Mental DMG buff after the wearer fires an Ultimate, which lines up perfectly with Fadia's HP-scaling kit. Unlike most S-Rank arcs, you can pick this one up for free during the main story.

Quick answer: Finish the Deal? Deal! main quest, then return to The Never-Ending Arachne weekly boss at the Ebisu Auction House in Unheard Shores (Hethereau) and beat it again to claim the Eternal Waltz Arc as a reward.

Eternal Waltz stats and skill

The Arc scales primarily on ATK with an HP% substat, and its passive is named Arachne. The skill effect grows with Mixing Level, but the base values are what most players will use first.

At Mixing Level 5, the passive scales to +32% Max HP and +18% Mental DMG for 10 seconds after Ultimate. The buff refreshes every time the wearer ults, so high-frequency Ultimate rotations keep it close to permanent uptime.

How to get Eternal Waltz in Neverness to Everness

The Arc is tied to the fourth main mission, Deal? Deal!, in which you fight The Never-Ending Arachne for the first time. The first clear progresses the story but does not drop the weapon. After the quest ends, the boss becomes a repeatable Anomaly Pilgrimage encounter, and that's where Eternal Waltz drops.

Step 1: Complete the prior main mission Love that Begins with Lies so that Deal? Deal! appears in your quest log automatically. The mission begins in Old Town and is gated to roughly Hunter Level 45 content.

Step 2: Play through Deal? Deal! until the Dance Until Dawn objective. Clear the five Level 35 Oddities first, then defeat the Level 45 Never-Ending Arachne and finish the remaining steps to wrap the quest.

Step 3: Travel to the Ebisu Auction House in the Unheard Shores district of Hethereau. Approach the front door to open the Anomaly Pilgrimage entry for the boss. The encounter is now repeatable on its weekly cooldown.

Step 4: Defeat The Never-Ending Arachne again. The Eternal Waltz Arc is awarded on a successful clear of this repeat fight, not the story version.

You'll know it worked when the Arc appears in your inventory under the Synthesis category and can be equipped on Fadia or any other Synthesis-type character.

Alternative source: Tri-Key shop

If you want extra copies for Mixing Level upgrades, Eternal Waltz is also stocked in the Arc Selection shop. The exchange uses Tri-Keys, which are earned through Annulith Processing and Hunter Exchange.

Boss fight notes for the Arachne refight

The repeat fight uses the same mechanics as the story version, so a clean run is mostly about pattern recognition. The Arachne is weak to Chaos, which makes Daffodill the strongest frontline pick. Pairing her with Psyche or Incantation units enables Esper Cycle reactions like Discord or Scorch, both of which carve through her break bar quickly.

• Flower shockwaves on the floor can be jumped over or Critical Dodged.
• The full-room laser pattern leaves visible safe gaps. Slip between the predictive lines instead of trying to dodge through them.
• Phase 2 plunges the arena into darkness. Stay inside the spotlight beams or your character freezes in place.
• Her telegraphed final strike in Phase 2 is always parryable. A successful parry opens a long damage window.

If you wipe, the issue is almost always one of three things: leaving the spotlight in Phase 2, eating the laser sweep without finding a gap, or attempting to dodge her parry-flagged attack rather than parrying it.

Why Eternal Waltz is best on Fadia

Fadia's Skill (Existence) and Ultimate (Agony to Euphoria) both scale off her Max HP, so the +20% HP from the Arac​hne passive directly increases her damage and her self-heal. The +10% Mental DMG window after Ultimate matches exactly when she's on field doing her empowered hit, and Mental DMG is the damage type her kit converts to. The result is a free signature-grade weapon for a limited 5-star unit, with no gacha pulls required.

The Arc also works as a generic HP-stick for any Synthesis character who needs survivability, but the Mental DMG clause is wasted outside of Fadia. If you don't run her, prioritize different S-Rank arcs and keep Eternal Waltz on the bench for when she joins your roster.

Ascension materials to Lv. 80

Eternal Waltz uses standard Synthesis ascension materials. The full path from Lv. 20 to Lv. 80 requires the totals below.

Once the Arc is equipped, slot Fadia with the Devil's Blood: Curse Cartridge set and a Psyche DMG Bonus main stat to round out the build, and her Ultimate windows will benefit from the buff every cycle.