Mortenax Blade — Honkai Star Rail Character Guide

Overview

HP-scaling Fire Nihility hybrid who deploys a Zone via Ultimate, layering DEF shred and Vulnerability while turning every ally attack into a debuff trigger. Self-tanks via 50% DMG reduction and chains free Follow-up Skills.

HP-scaling Fire Nihility hybrid who casts Ultimate to inflict Balefire Bind (DEF -30%, +50% DMG Taken) on all enemies and deploy a Zone that triggers his Infinite Fury state. While the Zone is active, every ally attack on an enemy reapplies Balefire Bind and generates a Charge; at 9 Charges (7 at E2), he fires a free Skill that counts as a Follow-up ATK and regenerates 25 Energy, looping into his own Ultimate. Every damage source scales on Max HP. Skill is Skill-Point-free, so the only SP cost in his kit is the Basic.

Key Mechanics

• All damage sources scale on Mortenax's Max HP — Basic 70% (140% enhanced), Skill 72% + 4x24%, Tenax Per Ignem 350%. ATK% is useless on him; CRIT body / HP% or Fire DMG orb / HP% or Energy Regen rope are the default mains, choosing CRIT Rate unless substats or teammates already solve his in-Zone CRIT Rate cap.
• Balefire Bind is a guaranteed application from Ultimate and from every ally attack on an enemy while the Zone is active (Talent), AND from every enemy hit on Mortenax (A4). EHR is not needed — there is no chance roll anywhere in the application chain.
• The A6 conditional branches based on whether a second Nihility character is in the team. With another Nihility ally, the +75% Ultimate DMG branch fires and benefits every ally (especially Ultimate-reliant carries). Solo-Nihility teams instead route the +75% to Mortenax's own damage, turning him into a stronger personal carry.
• The Zone's SPD-70 countdown gives ~143 Action Value of Infinite Fury uptime per cast; wave resets in Memory of Chaos refresh the countdown. The 80-Energy overflow plus A2's 75% energy floor on Zone-dispel mean Mortenax routinely re-Ults within a turn of the Zone ending.
• Mortenax pulls aggro under the Zone and takes 50% reduced DMG — combined with high HP scaling and the no-die killing-blow guard, he can pseudo-sustain teams that would otherwise need a healer. Dedicated healers still raise his ceiling because he scales on the HP they buff and heal.

Mortenax Blade Investment Priority

1. E1 — Strong first stop: 20% All-Type RES reduction on every enemy in the Zone is a rare, universally applicable multiplier that benefits any teammate regardless of element. E1 beats the signature light cone for amp value, and the 15% countdown delay per extra Skill stretches Zone uptime in slower teams. It is also on the way to E2.
2. E2 — Tags ally Ultimates as Follow-up ATKs (unlocking FUA buffs and FUA-leveraged sets), grants +75% ally Follow-up ATK DMG inside the Zone, and lowers the Talent extra-Skill threshold from 9 to 7 Charges (~22% more extra-Skills). The natural ceiling stop and one of the strongest E2s in the game.
3. LC S1 — Signature solidifies Mortenax's personal-damage chassis with +30% Max HP, the Purgatory CRIT DMG layer, and 20 Energy per wave for a fast first-cycle Ult. For pure team amp it sits behind Cipher's light cone and Tutorial Mission and only modestly ahead of the budget Nihility cones, so it lands after E1 and E2 unless Mortenax is played as a main carry.

Mortenax Blade Relics and Stat Targets

Recommended: Divine-Querying Master Smith with Sprightly Vonwacq

Stat targets: SPD 134 default; 140.1 for 2 actions in-zone (also the AS 7-turn / 500-AV breakpoint), CRIT Rate 80% pre-combat (60% with a +20% CRIT Rate teammate), CRIT DMG 120-140% pre-combat, HP 5,000-7,000 in-combat (5,000 floor for Bone Collection)

Main stats: Body: CRIT Rate / CRIT DMG · Feet: SPD · Sphere: HP% / Fire DMG · Rope: HP% / Energy Regen

Best Mortenax Blade Light Cones

• Lies Dance on the Breeze (Best in Slot): Off-character signature and the best pure-amp light cone for Mortenax once he reaches 170 SPD. +18% SPD plus up to 44% DEF shred at S5 (Bamboozled + Theft) stacks additively with Balefire Bind's 30% — over 70% combined DEF reduction from Mortenax alone before any other source. Needs roughly 30% Effect Hit Rate for full uptime, a real cost on a stat line already split between HP and CRIT. Best when Mortenax is purely buffing a frontloaded carry; it gives him no HP or CRIT, so his personal damage drops.
• Before the Tutorial Mission Starts: Herta Store 4-star and the best overall utility light cone for sub-DPS Mortenax. Its energy-on-debuffed-attack mechanic triggers continuously inside the Zone (Balefire Bind keeps every enemy debuffed), unlike the signature's once-per-wave energy clause, shortening his Ult cycle to as little as one turn and pairing especially well with Eagle 4pc. The energy-density advantage scales unusually hard with superimposition — a maxed copy out-paces an unmaxed Cipher light cone on repeat-Ult Mortenax, which is why its S5 is authored above the signature's S1. The EHR stat line is wasted on him, and a teammate must apply DEF-down before his turn for the energy trigger to fire pre-Zone.
• Reforged in Hellfire: Signature light cone. Best for Mortenax's personal HP-scaling damage and CRIT-leveraged dual-carry shells where the generic CRIT DMG layer lands on the partner's hits. Provides +30% Max HP (amplifies every damage source), 20 Energy at the start of his turn once per wave (a fast turn-1 Ult into the Zone), and the Purgatory state (target takes +30% CRIT DMG from any attacker plus an additional +30% from the wearer). For pure team amplification it is not the ceiling — Cipher's light cone out-amps it at 170 SPD and Tutorial Mission out-cycles it — so it is recommended mainly when Mortenax is played as a main carry or alongside a CRIT-leveraged carry.
• Holiday Thermae Escapade: 4-star Nihility battle-pass cone ("Chill Out"). Unconditional +16% to +32% wearer DMG (S1-S5) plus an on-attack Vulnerability that stacks additively with Balefire Bind on the same DMG-taken bucket. No DEF shred, so it does not compete with Cipher's light cone for the dedicated-amp slot. A clean budget amp pick that combines personal and team-wide damage without the heavy EHR requirement of the DEF-shred cones, though application is still smoother with some EHR.

Mortenax Blade FAQ

What relics should Mortenax Blade use?

Mortenax Blade's recommended relic setup is Divine-Querying Master Smith with Sprightly Vonwacq, with stat targets around SPD 134 default; 140.1 for 2 actions in-zone (also the AS 7-turn / 500-AV breakpoint), CRIT Rate 80% pre-combat (60% with a +20% CRIT Rate teammate), CRIT DMG 120-140% pre-combat.

What is the best light cone for Mortenax Blade?

Lies Dance on the Breeze is the top listed light cone for Mortenax Blade. Off-character signature and the best pure-amp light cone for Mortenax once he reaches 170 SPD. +18% SPD plus up to 44% DEF shred at S5 (Bamboozled + Theft) stacks additively with Balefire Bind's 30% — over 70% combined DEF reduction from Mortenax alone before any other source. Needs roughly 30% Effect Hit Rate for full uptime, a real cost on a stat line already split between HP and CRIT. Best when Mortenax is purely buffing a frontloaded carry; it gives him no HP or CRIT, so his personal damage drops.

How should I invest in Mortenax Blade?

Mortenax Blade's first listed investment priority is E1. Strong first stop: 20% All-Type RES reduction on every enemy in the Zone is a rare, universally applicable multiplier that benefits any teammate regardless of element. E1 beats the signature light cone for amp value, and the 15% countdown delay per extra Skill stretches Zone uptime in slower teams. It is also on the way to E2.

Important Notes

• Skill is locked at 1 HP — Mortenax's extra-Skill Follow-up ATK and base Skill both stop firing when his current HP hits 1. Long fights (Anomaly Arbitration, late MoC cycles) require sustained healing or a partner that scales him back up; sustainless setups eventually wall out.
• Shielders alone do NOT solve the 1-HP issue because Mortenax's Skill cost reduces HP directly (it does not eat shield first). Aventurine and similar shielders prevent enemy damage but not Mortenax's self-cost — pair shielders with a healer or rely on the Dan Heng Permansor Terrae signature light cone's self-heal-on-attack workaround.
• Damage is AoE-centric — single-target fights see noticeably lower personal damage because the Skill's 4x24% bounces re-roll into the same target only sometimes. Partner with Tribbie E1 (single-target Zone Additional DMG funneling) or accept the trade-off in single-target boss fights.
• Base Ultimate cost is 160 Energy — high for the path. The 80-Energy overflow plus the 120-Energy floor regenerated at battle start and on Zone-dispel offset this (leaving him at most ~40 Energy from his next Ult); expect roughly one Ult every other turn in high-frequency teams, every 2-3 turns in slower teams.
• A6 conditional changes based on team composition: with another Nihility ally, the team gets +75% Ult DMG (great for Acheron); without a second Nihility, Mortenax keeps the +75% for himself (better for solo-Nihility FUA shells with Ashveil). At E0, single-Nihility FuA teams do NOT get an ally FuA-DMG team buff from his A6 — that buff is exclusive to E2.
• A0 Ultimate is NOT classified as a Follow-up ATK — that classification only arrives at E2. Pre-E2, Mortenax's own Ult does not receive FUA-tagged buffs from Ashveil, Salsotto's FuA branch, or Eagle 4pc trigger.