HSR Mortenax Blade — Best-in-Slot Build for Version 4.3

Mortenax Blade — also known as Blade SP — arrived in Honkai: Star Rail Version 4.3 on June 1, 2026, and he's already one of the most flexible characters in the game. A Fire-element Nihility unit who scales on HP, debuffs enemies, and amplifies team damage through his Bounded Field. Here's the complete build guide: best Light Cone, best Relics, optimal stats, top teams, and how to play his Infinite Fury state.

🔥 Who Is Mortenax Blade?

Mortenax Blade is the 5-star Phase 1 character of Version 4.3 "The Lethe Below the Living." He's a Fire-element character on the Path of Nihility, sharing visual identity with the original Blade but with an entirely new combat kit centered around HP scaling, debuffs, and Zone-based amplification. Where the original Blade was a pure follow-up DPS on the Path of Destruction, Mortenax Blade is a hybrid sub-DPS and support — a generalist debuffer who deals respectable damage of his own while substantially amplifying the team's overall output.

His banner runs from June 1 to June 24, 2026, alongside the Yao Guang (Elation: Physical) rerun. After his debut, Mortenax Blade will likely become a long-term meta staple due to how broadly his kit fits into existing team compositions — particularly Nihility-focused teams running Acheron or Ashveil.

⚔️ Understanding Mortenax Blade's Kit

Mortenax Blade's kit is built around a four-part loop: deal HP-scaling damage, apply debuffs, charge his Ultimate, then enter Infinite Fury for amplified output through his Bounded Field.

Basic Attack: Deals Fire damage equal to 50% of Mortenax Blade's Max HP to one designated enemy, applying Taunt for 1 turn. Since damage scales on Max HP, stacking HP is the foundation of every Mortenax Blade build.

Skill: Consumes a percentage of his own HP to deal Fire damage to all enemies, then deals additional Bounce damage to a single target. This is his primary damage skill and the source of most of his pre-Ultimate output. The HP consumption is the catch — he needs a strong sustain unit on the team to avoid death.

Ultimate — "Fornax Ex Corpore": Deploys a Bounded Field (called the Zone) and enters the Infinite Fury enhanced state. During Infinite Fury, he gains a brand new skill set, applies Balefire Bind to enemies in the Zone, and benefits from significant damage amplification on his rotation. The Ultimate also provides a damage increase to all allies when at least one other Nihility character is on the team — making him a natural pair with Acheron, Ashveil, and other Nihility units.

Talent: Generates Charge whenever allies attack enemies in the Zone. Charge converts into extra Skill activations that function as Follow-Up attacks, adding significant damage on top of his base rotation. The more allies attack inside the Zone, the more Charge stacks, and the more Follow-Up Skills trigger.

💎 Best Light Cone — Reforged in Hellfire

Mortenax Blade's signature Light Cone, Reforged in Hellfire, is by far his best option. It grants:

• 30% HP boost — directly increases his damage output since his kit scales on HP
• 20 Energy regeneration at turn start — accelerates Ultimate availability significantly
• Skill attack debuff — applies an additional debuff when attacking enemies with Skill, stacking with his existing Balefire Bind for higher team damage

The Light Cone is built around exactly what Mortenax Blade wants: HP scaling, faster Ultimate access, and more debuff coverage. There's no genuine alternative at his signature's power level.

If you can't pull the signature, look for HP-scaling or Nihility-focused 4-star options as placeholders. Mortenax Blade still functions without his signature — he just doesn't hit his ceiling.

🏛️ Best Relic Set — Divine-Querying Master Smith

The new Divine-Querying Master Smith set introduced in Version 4.3 is Mortenax Blade's best-in-slot Relic set by a significant margin. The set bonuses give him:

• 2-piece: HP% bonus — directly amplifies his damage scaling
• 4-piece: Crit DMG increase + the Comburent effect, which provides a 15% damage bonus to allies. This is the cornerstone of his role as a team amplifier rather than a pure damage dealer

The Comburent effect is the deciding factor — it transforms Mortenax Blade from a sub-DPS into a true team damage multiplier. Other Relic options exist, but none combine HP, Crit DMG, and team-wide damage amplification the way the Smith set does.

Alternative Relic Sets:

• Pioneer Diver of Dead Waters — Solid offensive alternative if you can't farm Smith. His personal damage stays competitive, but you lose the team Comburent buff
• Smith's Fire Beast Mask — Another Smith variant that pairs well with his kit, also providing HP% and Crit DMG

🌟 Best Planar Ornament — Sprightly Vonwacq

Sprightly Vonwacq is the top Planar Ornament for Mortenax Blade. The set provides Energy Regeneration and a passive Action Advance — both of which accelerate his Ultimate uptime. Since most of his damage output and team amplification comes from being in Infinite Fury state, faster Ultimate access directly translates to more damage windows per cycle.

Alternative Planar Ornaments:

• Bone Collection's Serene Demesne — If you're struggling to reach the 6,000–7,000 HP threshold for his damage scaling, this set's HP focus helps you hit the breakpoint
• Duran, Dynasty of Running Wolves — Strong choice when running with Follow-Up DPS like Feixiao
• Inert Salsotto — Crit Rate boost option, helpful if you have HP/Crit DMG covered elsewhere
• Lies Dance on the Breeze / Resolution Shines As Pearls of Sweat — Both function as exceptional alternatives

📊 Optimal Stats Priority

Build Mortenax Blade around these stat targets:

1. HP: 7,000+ — Highest priority. His entire damage profile scales on Max HP. Below 6,000 HP, his damage feels meaningfully weaker. Above 7,000, he hits hard consistently
2. Crit Rate: 80%+ — His Ultimate grants him 100% Crit Rate in the Zone, but you want consistent crits before Ultimate too
3. Crit DMG: 200%+ — Standard high-DPS target. Pair with high HP for maximum damage scaling
4. Speed: 134+ — Standard benchmark for endgame Nihility units to fit comfortably in standard rotation orders
5. Energy Regeneration: As high as possible — Ultimate uptime is the build's gating factor. Reforged in Hellfire + Sprightly Vonwacq + ERR substats stack to keep his Ultimate cycle tight

The most important breakpoint: 7,000 HP minimum for endgame content. Below that, the build feels under-tuned regardless of what else you've stacked.

👥 Best Teams for Mortenax Blade

Mortenax Blade is a generalist — he fits into many compositions, but his strongest teams pair him with:

Acheron Team — Top-Tier Synergy: Acheron is the premier Nihility carry, and Mortenax Blade enables her ceiling through his debuffs and the Nihility-team Ultimate damage bonus. Add Aventurine for sustain and Pela or Silver Wolf for additional debuff stacking. This is the most-recommended Mortenax Blade team composition for endgame content.

Ashveil Team — Newer Meta Pick: Ashveil's hybrid debuff + damage kit synergizes naturally with Mortenax Blade. The two debuffers stack debuffs efficiently, and both contribute meaningful damage. Strong choice if you have Ashveil built.

Feixiao Team — Follow-Up Focus: Feixiao's follow-up attack frequency benefits enormously from Mortenax Blade's Comburent buff and Zone, while her constant attacks generate Charge for his Talent. The two scale into each other naturally.

Castorice Team — HP Drain Synergy: Mortenax Blade isn't Castorice's BiS support, but his HP drain helps charge her Ultimate, and he has natural synergy with her other teammates like Tribbie and Hyacine. Workable backup pairing.

Hyacine — The Best Sustain: Hyacine is currently the optimal sustain for any Mortenax Blade team. She naturally reaches high Speed, provides Max HP buffs that directly scale his damage, and her Little Ica attacks generate consistent Charge for his Talent. If you have Hyacine, build her into every Mortenax Blade team.

🎯 Pull Strategy and Eidolon Recommendations

For most Trailblazers, E0 Mortenax Blade with his signature Light Cone is the optimal investment target. E0S1 covers nearly his entire ceiling for endgame content like Memory of Chaos and Apocalyptic Shadow.

Eidolons are worth considering if you have spare Stellar Jade after securing E0S1:

• E1 — Strong general improvements to damage output and Zone uptime
• E2 — Significant boost to Follow-Up attacks, making him fit naturally into Follow-Up-focused teams alongside Feixiao, Robin, or Topaz
• E6 — Mostly for completionists. Diminishing returns relative to investment for most Trailblazers

If you're choosing between Mortenax Blade and Yao Guang (Phase 1 rerun), prioritize Mortenax Blade unless you specifically need a Physical Elation carry. Yao Guang is a strong character, but Mortenax Blade is a longer-term meta investment because of how broadly his kit fits into existing teams.

🛒 Build Mortenax Blade to His Ceiling

Mortenax Blade's full potential takes serious gear investment, optimal Relic farming, and team building around his Zone mechanics. Trailblazers ready to push Memory of Chaos and Apocalyptic Shadow with the new Version 4.3 meta can explore trusted Honkai: Star Rail Accounts with strong existing rosters ready for Mortenax Blade integration, accelerate every Relic and Trace material farming session with expert Honkai: Star Rail Hourly Services, or clear every piece of Version 4.3 endgame content effortlessly through reliable Honkai: Star Rail Boosting.

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