Nestbound Bird Boss Guide: Tears Beneath the Mask Arc, Call of the Lost Commission, Cosmos Strategy, Hotori Vulnerable Window

Quick answer: The Nestbound Bird / Call of the Lost is on the rooftop of the Pink Paws Bank in the New Hereland district (climb the exterior stairs and look for the red torii gate), and its weakness is Cosmos. It is extremely aggressive with high melee damage, handled with Parry + Critical Dodge. After you take off 30% HP, Hotori intervenes → the long vulnerable window is your all-out DPS window. First clear guarantees the Tears Beneath the Mask S-rank Arc (Skia’s signature weapon; the Ultimate applies an 18–30% enemy damage-reduction debuff).

ℹ Naming note: in-game English may differ from community fan translations; this site lists both where relevant. The Tears Beneath the Mask effect is an “enemy damage-reduction debuff,” not “active party-wide damage reduction” — describe it precisely.

“A mother bird calling out to lost children in a gentle female voice” — the Nestbound Bird is one of the most emotionally charged bosses in NTE, and it drops Skia’s signature weapon, “Tears Beneath the Mask” (a party-protection masterpiece). This guide covers the location, moveset, the Hotori vulnerable window, and Cosmos teams all in one place.

1. What is the Nestbound Bird

Item	Details
Name	Nestbound Bird (Avian Anomaly)
Anomaly Commission	Call of the Lost
Monster type	A giant masked Avian Anomaly
Location	New Hereland district, south side of Oia Avenue, the high-rise with a rail line running through the building — rooftop of the Pink Paws Bank headquarters; the trigger is the floating red torii gate on the roof

Lore background (the tragic theme)

The Nestbound Bird is a “mother bird that nests deep in the shadows,” calling out to lost children in a gentle, sweet female voice and asking whether they would like “to become my child”; if a poor child agrees, they stay in the nest forever.

The flavor text on the drop material “Nest Guard Fragment” reads: “If only I could find those children…” — a classic “imprisonment in the name of love” tragic narrative.

2. Unlock / trigger conditions

1. Progress the main story to open the New Hereland district
2. Open the Anomaly Commission board at the bottom-right of the map and accept “Call of the Lost”
3. Track the quest → teleport to the area near the phone booth on the right side
4. ⚠️ Climb up the exterior stairs of the building floor by floor (you can pause at the “rail floors” midway to recover stamina)
5. Reach the top-floor red glow / red torii gate point and interact to start the fight
6. After defeating it, you can rechallenge on the same rooftop without re-running the quest line

3. Element and weakness

• Weakness element: Cosmos — bring at least one Cosmos character to significantly speed up the break
• Resistances: no specific resistances listed (defer to in-game)

4. Moveset (complete)

The boss is extremely aggressive, favoring “fast combo chains” of continuous barrages, with very high melee damage.

Phase 1

Move	Counterplay
Double-wing sweep	Dodge
Stomp → ring AoE	Dodge outside the ring
Twin-feather throw → Stomp	Dodge
Ground shockwave → dive slam	Dodge
Triple beam → Stomp	Dodge
Backhop → charged special	Open distance
Multi-hit screech → homing missiles	Reposition by the warning circles
Airborne triple combo (bomb rain → rapid fire → dive lunge)	Dodge the bomb rain / rapid fire; Parry the dive lunge

Phase 2 (from around 50% HP)

Move	Counterplay
Converging walls + mask beam	Move to avoid the walls
Double homing attack → Stomp	Dodge + Parry the Stomp

Parry-able vs dodge-only

• ✅ Parry-able: the dive lunge at the end of the triple combo, and the Stomp at the end of various combos → a successful parry briefly breaks the boss and opens a counterattack
• ❌ Dodge-only: bomb rain, rapid fire, homing missiles, etc.; reposition based on the ground warning circles

⭐ Core mechanic: Hotori intervention → long vulnerable window

• After taking off about 30% HP, a cutscene triggers in which Hotori joins the fight
• Once the cutscene ends, the Nestbound Bird enters a long vulnerable state → an all-out DPS window
• It is best to unload your Ultimates and burst skills here

5. Drops and rewards

Guaranteed first clear

• 🏆 Tears Beneath the Mask — an S-rank Gas Arc, Skia’s signature weapon / Sakiri’s endgame pick
  • 512 base ATK, +27.5% ATK (defer to in-game)
  • Effect “Warning Gaze”: after the wearer’s Ultimate (Orbit Finale) hits an enemy, it reduces the damage that enemy deals (Lv1 −18% / Lv2 −21% / Lv3 −24% / Lv5 −30%) for 20 seconds, non-stacking

Common / repeat drops

• Nest Guard Fragment (ascension material)
• Hunter EXP, Beetle Coins, Arcane Threads / Magic Threads, Funce, Crystals, etc.

Weekly rechallenge + high-risk tiers

After clearing the standard difficulty, you unlock 6 escalating high-risk tiers (around Lv45–90), each adding mechanics like Overload, Flash Moment, Hunter’s Gaze, Perfect Rhythm, and so on. The weekly cap is per in-game values.

For full Arc details, see the Complete Skia Build Guide.

6. Recommended teams (Cosmos weakness)

Bring at least 1 Cosmos character to break, and build around Synthesis reactions with Genesis Flower / Remora / charge Espers.

Endgame build

Nanally (Main DPS) + Jiuyuan + Esper Zero (Cosmos lane-shift to trigger Genesis) + Sakiri (group + buff)

Routine: Sakiri groups enemies → Nanally holds the field for damage → Esper Zero lane-shifts to trigger Genesis → Nanally’s Orbit burst → Jiuyuan cleans up

Free-to-play / launch build

Adler (lane-shift shielding) + Haniel (lane-shift ATK buff) + Chiz (on-field Main DPS, Cosmos) + Esper Zero (reaction trigger)

If Jiuyuan isn’t available, Mint can substitute

Game8 / GameWith call out the following as especially effective against this boss: Esper Zero, Chiz, Sakiri; they also list Hathor, Skia, and Mint.

7. Combat tips + common beginner mistakes

Tips

1. Afraid of getting one-shot in melee → lean fully on Critical Dodge + Parry: precisely parry the Stomp / dive lunge to break and counter, and dodge the bomb rain / rapid fire / homing missiles by reading the warning circles
2. ⭐ Hold your burst until the Hotori vulnerable window: the window after the 30% HP cutscene is the biggest DPS opportunity
3. Bring a Cosmos character to speed up the break, shortening the dangerous high-damage phases
4. Bring a damage-reduction / control system (Remora) to further suppress the boss’s output

Common beginner mistakes

❌ Mistake	✅ Correct
Looking for the boss at street level	It’s on the Pink Paws Bank rooftop — climb the exterior stairs and find the red torii gate
Blindly tanking the melee combos	Not dodging or parrying gets you killed extremely easily
Still dodging / defending during the vulnerable window	After the cutscene you should go all-out — don’t idle and waste the DPS window
Bringing no Cosmos	Slow break, the dangerous phase drags on
Equipping the Arc as “active party-wide damage reduction” on the wrong character	It’s an Ultimate-triggered enemy damage-reduction debuff, so equip it on a character with Ultimate damage / a trigger rotation (Skia above all)

8. Related guides

• Complete Anomaly Boss Bestiary — overview of all 18 bosses
• Serenetti / Mammon / Headless Rider / Beat King — other popular bosses
• Complete Skia Build Guide — owner of Tears Beneath the Mask
• Complete Signature Weapon (Signature Arc) Guide — full comparison of Tears Beneath the Mask
• Elemental Reaction System — Genesis reactions

FAQ

Nestbound Bird data compiled from public sources including Game8, GameWith, Game Rant, Nerdschalk, The Profaned Geek, Icy Veins, BlogAndGuide, Entertainment Taxi, 4Gamers, LDPlayer, and Bahamut. In-game names, Arc stats, and weekly reward caps should be confirmed against the live game.