Phantom Blade Zero Fiend Saws Weapon Guide

TL;DR

Fiend Saws are a dual-wield weapon dropped from Mu Xiaokui’s full three-phase encounter in the Village of Lu during Chapter 3.
They are missable — you must interact with all five of Mu Xiaokui’s ribbons before the fight to unlock the third phase and its rewards.
Every hit builds up Fiend-Aura Erosion on the enemy. When the gauge is full, it erupts and drains their HP — on top of normal attack damage.
Power Surge (Fiend Form) makes all attacks unblockable for 10 seconds and deals extra damage against guard-broken enemies. Always activate it after a guard break.
Level 5 and Level 15 perks let you transform the Erosion gauge into Azure Erosion (Sha-Chi drain) or Crimson Erosion (damage burst).
Level 25 perk, Corrosive Severance, lets you trigger early eruption on all enemies at any time — a massive damage tool.
Soul Tempering with the Heel Reinforcement Part unlocks Endless Fiend Form — all attacks become unblockable for 3 seconds after any eruption.
Widely considered the best overall weapon and best dual-wield weapon in the game. Pairs perfectly with the Outlaw Warblade.

Table of Contents

What Are the Phantom Blade Zero Fiend Saws?

The Fiend Saws are one of the most powerful weapons in Phantom Blade Zero — and the top-ranked dual-wield option by most players who have tested the full weapon roster. The game describes them as a pair of unique blades once wielded by Jade Dancer with her legs. Soul now carries them in hand, but their fiend-aura remains intact and just as deadly.

What makes the Fiend Saws stand out is a damage system that builds on top of your normal attacks. Every hit stacks Fiend-Aura Erosion on the enemy. Fill the gauge and it erupts, eating directly into their HP. That’s extra damage on top of everything else you’re already dealing — and with fast dual-wield attack strings, the gauge fills faster than you’d expect.

Then there’s Fiend Form. Pop the Power Surge and every attack you land becomes unblockable for 10 seconds, with bonus damage against guard-broken enemies. Activate it right after cracking a boss’s guard and you can melt a significant portion of their health in that window alone.

Players rate the Fiend Saws as one of the best weapons overall in Phantom Blade Zero — and for good reason. The combination of raw speed, burst damage from Erosion eruptions, and the devastating Fiend Form window gives it a damage ceiling few other weapons can match.

Fiend Saws

How to Get the Fiend Saws in Phantom Blade Zero — Don’t Miss Them

The Phantom Blade Zero Fiend Saws are obtained from Mu Xiaokui’s full boss encounter in the Village of Lu during Chapter 3 (Heartless Remnants). The critical word here is full. This weapon is missable, and it’s one of the most commonly missed weapons in the game.

Step 1 — Find and Interact With All Five of Mu Xiaokui’s Ribbons

Before you fight Mu Xiaokui, the final boss of the Village of Lu, you must track down and interact with all five of her ribbons scattered throughout the region. These are connected to a side quest called Young Mistress. Collecting all five unlocks the third phase of her boss fight — the phase where both the Fiend Saws and the Wild Oriole Sword become available as rewards.

Skip this step and the third phase simply doesn’t happen. The weapons never drop. You’ll complete the chapter and move on without ever knowing what you missed. The fifth ribbon is located just before the boss fight itself, so if you’re already at four, make one last check in the area before engaging.

Step 2 — Complete the Full Three-Phase Mu Xiaokui Encounter

With all five ribbons found, Mu Xiaokui’s fight becomes a three-phase encounter:

Phase 1 and Phase 2 — Direct fights against Mu Xiaokui herself.
Phase 3 — Her bodyguards Jade Dancer and Iron Fiend join together for a simultaneous duo fight. Completing this phase is what actually rewards the Fiend Saws.

The duo fight is legitimately tough. Jade Dancer is fast and mobile, while Iron Fiend hits heavily. Try not to let both flank you at once. Focus one target, use the environment to separate them, and don’t get greedy with combos when both are at close range.

For more on the Village of Lu and other weapons from this region, check out our Wild Oriole Sword weapon guide and the Tianxuan Bronze Sword weapon guide.

Fiend Saws Stats and Base Properties

Here’s what the Fiend Saws look like at their base level:

Type: Dual-Wield
Base Damage: 302
Base Guard Break: 120
Attack Speed: Fast
Core Perk: Fiend-Aura Erosion — each hit builds the gauge, and when it’s full, it erupts and drains the enemy’s HP
Power Surge: Fiend Form
Soul Temper Material: Heel Reinforcement Part

The 302 base damage is among the highest in the dual-wield category. The reach on the attacks is also surprisingly long for a dual-wield weapon — you can hit enemies at a distance that feels closer to a one-handed sword. That combination of range, speed, and high damage makes the Fiend Saws feel genuinely oppressive in extended fights.

Fiend-Aura Erosion Explained — How the Damage System Works

This mechanic is the engine of everything the Fiend Saws do. Understanding it completely changes how you play with this weapon.

How It Builds

Every hit you land with the Fiend Saws adds to an Fiend-Aura Erosion gauge on the enemy. The gauge tracks independently for each target. Once built, the accumulated Erosion lasts 20 seconds before it resets — so you don’t need to fill it instantly, but you do need to stay active on the same enemy to maintain your progress.

What Happens When It Erupts

When the Fiend-Aura Erosion gauge reaches full, the aura erupts automatically and directly depletes the enemy’s HP. This damage isn’t blocked or mitigated by their guard — it goes straight through. Against bosses with high defense or large health pools, this eruption burst is a significant chunk of damage on top of everything your normal attacks are dealing.

Altering the Erosion Type With Higher Perks

Once you upgrade the Fiend Saws further, you gain two charged attacks that transform the base Fiend-Aura Erosion into more specialized forms before it erupts:

Azure Erosion (from Charged Onslaught at Level 5) — A charged combo that changes the Erosion into one that depletes more of the enemy’s Sha-Chi when it erupts. Useful for keeping bosses or tough enemies starved of their energy bar.
Crimson Erosion (from Charged Frenzy at Level 15) — A charged spinning Sha-Chi slash combo that converts the Erosion into one that deals increased direct damage when it erupts. This is the higher-damage option and the one most players prefer for boss fights.

The smartest use of this weapon is building the Erosion gauge with fast light attacks, then using Charged Frenzy to convert it to Crimson Erosion right before it erupts — maximizing the damage burst from every single gauge cycle.

Power Surge — Fiend Form

The Fiend Saws’ Power Surge is called Fiend Form, and it’s one of the best Power Surges in the game. Here’s exactly how it works:

Costs 1 Sha-Chi Essence to activate.
Lasts 10 seconds.
During Fiend Form, all attacks become unblockable — they go through even if the enemy is guarding.
Attacks deal increased damage against guard-broken enemies during the window.
While in Fiend Form, pressing the Power Surge button again triggers a powerful follow-up attack with no additional Sha-Chi cost. This ends Fiend Form immediately after, so save it for when you’ve gotten full value from the window.

The key to using Fiend Form well is timing. Don’t activate it randomly — activate it right after breaking an enemy’s guard. During Fiend Form, every attack is unblockable and hits harder against guard-broken targets. Combine that with the fast attack strings of a dual-wield weapon and those 10 seconds can remove a massive portion of a boss’s health bar.

Activating Fiend Form before the guard is broken wastes the bonus damage bonus. Be patient. Break the guard first, then go.

All Fiend Saws Upgrade Perks — Every Level Milestone

Perks unlock at Levels 5, 10, 15, and 25. The Fiend Saws have one of the most layered perk progressions in the entire game — each milestone meaningfully changes how the Erosion system works.

Level 5 — Charged Onslaught and Corrosion Burst

Charged Onslaught is the first major addition to the moveset. During a combo, hold the light attack button to charge, then release for a rapid series of crossing slashes that infuse Fiend-Aura into the wounds. This transforms whatever Fiend-Aura Erosion is currently on the enemy into Azure Erosion, which depletes more of the enemy’s Sha-Chi when it erupts.

Corrosion Burst (also a Level 5 unlock) slightly increases the damage dealt by Fiend-Aura Erosion and all its altered forms when they erupt. It’s a passive improvement that makes every eruption deal a bit more pain — nothing dramatic, but it stacks with everything else.

Level 10 — Passive Enhancement

Level 10 improves the passive effectiveness of the Fiend-Aura Erosion system, making the gauge build slightly more efficiently and the weapon more consistent in sustained combat. This is the free-refund cutoff — test the Fiend Saws up to here with no cost before committing materials past this point.

Level 15 — Charged Frenzy

This is one of the most impactful perks on the weapon. Charged Frenzy adds another charged attack option: during a combo, hold the heavy attack button to charge up a rapid series of sweeping, spinning Sha-Chi slashes that drive Fiend-Aura deep into the bone. This transforms the Erosion into Crimson Erosion, which deals significantly increased damage when it erupts compared to the base version.

Most experienced players prefer Crimson Erosion over Azure Erosion for boss fights. The extra damage burst from Crimson Erosion outweighs the Sha-Chi drain of Azure Erosion in most encounters. Get this weapon to Level 15 as early as you can — it’s where the Fiend Saws start feeling truly elite.

Level 25 — Corrosive Severance

The game-changing late-game perk. Corrosive Severance lets you press a dedicated button to manually trigger an early eruption of Fiend-Aura Erosion, Azure Erosion, or Crimson Erosion — on all enemies at once — before the gauge naturally fills.

This removes the wait entirely. You build the gauge, convert it to Crimson Erosion with Charged Frenzy, then manually detonate it with Corrosive Severance right in the middle of a combo. No waiting. No timing issues. You control exactly when the burst goes off, and you can chain this into follow-up attacks during the same offensive window for devastating combo damage.

Against bosses, Corrosive Severance lets you sync eruptions with Fiend Form — pop Fiend Form after a guard break, charge up Crimson Erosion, trigger Corrosive Severance mid-combo, and you’re dealing unblockable bonus damage plus a Crimson Erosion burst in the same 10-second window. It’s a serious damage output loop.

Soul Tempering the Fiend Saws — Endless Fiend Form

Soul Tempering the Fiend Saws requires the Heel Reinforcement Part. To get it, you need to return to the Crimson Forest later in the game. Specifically:

Speak with Mu Xiaokui on the Crimson Forest’s Sha-Chi Tower rooftop, accessed beyond the Friendly Shadow Warden. This is a later-game area available after significant story progression.
After that conversation, talk to Jade Dancer. She challenges you to a sparring match — a rematch duo fight against Jade Dancer and Iron Fiend together.
Win the sparring match to receive the Heel Reinforcement Part.

The Soul Tempering effect unlocked is called Endless Fiend Form:

Endless Fiend Form: After Fiend-Aura Erosion (or any of its altered forms) erupts on an enemy, all attacks against that enemy become unblockable for 3 seconds.

This is exceptional. Every single eruption now triggers a 3-second unblockable window. Combined with Corrosive Severance at Level 25, you can detonate eruptions on demand and chain those unblockable windows through an entire fight. The synergy between Endless Fiend Form and Corrosive Severance is one of the strongest damage setups in Phantom Blade Zero.

Soul Tempering is done through Myst in Pengzhen, available from Chapter 4. It costs 5,000 Remnant Dust plus the Heel Reinforcement Part. As always — Soul Tempering is permanent and cannot be undone. Make sure the Fiend Saws are your long-term weapon before committing.

Best Weapon Combinations With the Fiend Saws

You carry two main weapons at once in Phantom Blade Zero. The Fiend Saws work best as your primary damage dealer. Here’s what to pair them with:

Fiend Saws + Outlaw Warblade

This is the most recommended pairing in the game. The Fiend Saws handle all the burst damage — fast attacks, Erosion buildup, Fiend Form windows. The Outlaw Warblade covers everything the Fiend Saws lack: healing through light attacks, a lifesteal Power Surge with a massive invincibility window, and strong defensive utility. When your health is low, switch to the Warblade to recover. When the enemy is guard-broken, switch to the Fiend Saws and go to work. The two weapons cover each other’s gaps almost perfectly.

Fiend Saws + White Serpent and Crimson Viper

For pure aggressive output, this is the standout offensive pairing. White Serpent and Crimson Viper excels at continuous attack chains and sustained pressure, building Sha-Chi quickly with fast dual-blade combos. Use it to maintain pressure and build your meter, then switch to the Fiend Saws when a guard break opens and activate Fiend Form immediately. Two fast, aggressive weapons with completely different damage types — one built for pressure, one built for burst.

Fiend Saws + Tianxuan Bronze Sword

A damage-plus-defense pairing. Use the Fiend Saws as your primary attacker during open opportunities. Switch to the Tianxuan Bronze Sword when you need to weather a sustained attack sequence — its reduced Sha-Chi blocking cost lets you hold your guard much longer without draining your energy, giving you better windows to get back on offense with the Fiend Saws.

Fiend Saws + Wild Oriole Sword

Both weapons are from the same Mu Xiaokui encounter, so you’ll often have them at the same time. The Wild Oriole Sword builds Sha-Chi fast with its speed and adds mid-range blade waves during Oriole Song. Use it to fill your meter and poke from range, then swap to the Fiend Saws for close-quarters burst damage and Fiend Form. Both weapons reward aggressive play, so this combination stays consistently offensive throughout a fight.

For a complete look at all dual-wield and other weapon options, see our complete Phantom Blade Zero weapons list.

Is the Fiend Saws the Best Weapon in Phantom Blade Zero?

The short answer is: for aggressive, damage-focused players, yes. Multiple weapon tier lists rank the Fiend Saws as the best dual-wield weapon and best overall weapon in the game. That’s a strong consensus.

The reasons aren’t hard to see. Fast attack speed, long reach for a dual-wield, high base damage, a status effect that adds bonus HP damage on top of normal attacks, a Power Surge that makes everything unblockable for 10 seconds, and a perk tree that keeps getting better through all the key milestones. Each upgrade makes the weapon feel more powerful, not just incrementally stronger.

The only real caveat is that the Fiend Saws reward players who understand their mechanics. Randomly spamming attacks builds Erosion slowly. Knowing when to use Charged Frenzy, when to activate Fiend Form, and when to trigger Corrosive Severance is what unlocks the weapon’s true damage potential. Once you learn the rhythm, the Fiend Saws can genuinely melt health bars in ways most other weapons can’t match.

Also worth remembering — they’re missable. If you rush through the Village of Lu without collecting all five ribbons, you don’t get them on that playthrough. That alone is reason enough to take your time in that region.

Upgrade Materials for the Fiend Saws

The Fiend Saws are a dual-wield weapon, so they use Twinned Metals and Solvents for standard upgrades. Higher tier upgrades require Polished Twinned Metal and Concentrated Solvent as you push toward Level 30.

Key checkpoints to keep in mind:

Up to Level 9: Free to reset at any bell. Good window to test the weapon before committing.
Level 10 and above: Requires a Weapon Reforge Talisman to reset. Think carefully before pushing past this point with any weapon you’re unsure about.
Level 15: Charged Frenzy and Crimson Erosion unlock. This is the recommended minimum investment — the weapon changes significantly here.
Level 25: Corrosive Severance unlocks. This is where the Fiend Saws reach their highest damage potential. Late-game materials are needed, but it’s worth the investment.

Start upgrading at Forge, the blacksmith NPC at the Weeping Creek Valley Outpost. Soul Tempering happens through Myst in Pengzhen, available from Chapter 4 onward.

Fiend Saws Tips and Tricks

Get all five ribbons before fighting Mu Xiaokui. No ribbons, no third phase, no Fiend Saws. This is the one step that causes the most players to miss this weapon permanently in a playthrough.
Always activate Fiend Form after a guard break, not before. The bonus damage against guard-broken enemies is significant. Activating it randomly wastes half the Power Surge’s value.
Use the follow-up attack inside Fiend Form wisely. Pressing Power Surge again during Fiend Form deals a strong bonus hit but ends the form immediately. Save it for the very end of the 10-second window, or for an emergency finish on a low-health enemy.
Prioritize Charged Frenzy at Level 15. Converting Erosion to Crimson Erosion before eruption is a significant damage upgrade. Get here as fast as your upgrade materials allow.
Corrosive Severance at Level 25 changes everything. Manual eruption control removes all the waiting from the Erosion system. Once you have it, you can sync eruptions with Fiend Form windows for a devastatingly consistent loop.
Pair with the Outlaw Warblade for a complete build. The Fiend Saws deal the damage. The Outlaw Warblade keeps you alive. It’s the most balanced and effective pairing in the game.
Don’t stack Azure and Crimson Erosion carelessly. Each charged attack overwrites the current Erosion type. Pick one approach and commit to it within each gauge cycle.
Soul Tempering is irreversible. Make sure the Fiend Saws are your primary weapon before spending the Heel Reinforcement Part and 5,000 Remnant Dust.
Endless Fiend Form pairs brilliantly with Corrosive Severance. Trigger an eruption on demand, get 3 seconds of unblockable attacks, keep the pressure going. At full investment, this is the strongest damage loop in Phantom Blade Zero.

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