A 3-notch charm that raises nail damage by 50%. The Grimm Troupe DLC Divine upgrade of Fragile Strength, costing 15,000 Geo to make permanent.
Unbreakable Strength is the most expensive Unbreakable upgrade in the Grimm Troupe DLC, at 15,000 Geo. Per the wiki, Divine in Dirtmouth eats the Fragile Strength charm and returns Unbreakable Strength, which carries the same +50% nail damage effect but no longer shatters when the Knight dies. The cost is high because Fragile Strength is the most-used Fragile charm in standard combat builds.
According to the wiki, Fragile Strength sits in Leg Eater's Fungal Wastes shop for 600 Geo (480 with Defender's Crest discount). The charm shatters on death and Leg Eater repairs it for 350 Geo per fix, which turns into a 12-fix break-even versus the 15,000 Geo Unbreakable conversion. Most players break even after 40 deaths.
The wiki specifies the 50% damage applies to every nail hit including Nail Arts (Cyclone Slash, Great Slash, Dash Slash). Spell damage and Sharp Shadow damage are NOT affected; only nail-derived damage gets the multiplier. The trio with Quick Slash and Mark of Pride forms the canonical 9-notch combat spine for Pantheon clears.
This guide covers the +50% nail mechanic, the Fragile-to-Unbreakable Divine conversion path, the 15,000 Geo break-even math, the Quick Slash + Mark of Pride synergy, and the Steel Soul recommendation tier.
+50% nail damage with no shatter-on-death penalty.
Trade Fragile Strength to Divine for 15,000 Geo in Dirtmouth (post-Grimm-Troupe summon).
Quick Slash + Mark of Pride for the 9-notch canonical combat spine.
Pure spell or Sharp Shadow builds; only nail-derived damage gets the +50% boost.Unbreakable Strength multiplies nail damage by 1.5. Per the wiki, the boost applies to every nail strike including up-slash, down-slash, forward slash, and all three Nail Arts. The damage uplift is multiplicative with other damage charms (Quick Slash speed boost, Mark of Pride reach boost), which is why the trio dominates Pantheon damage ceilings.
According to the wiki, the damage scales with the Knight's current nail tier. Pure Nail at 21 base damage becomes 31.5 damage per swing with Unbreakable Strength; Old Nail at 5 base damage becomes 7.5 damage per swing. The percentage multiplier stays constant; only the underlying nail tier changes.
The wiki specifies what the boost does NOT affect: spell damage (Vengeful Spirit, Shade Soul, Howling Wraiths, Abyss Shriek, Desolate Dive, Descending Dark), Sharp Shadow damage, and summon damage (Weaverlings, Hatchlings). Players who lean into those layers get zero benefit from Unbreakable Strength.
| Stat | Value |
|---|---|
| Notch cost | 3 |
| Damage boost | +50% nail damage |
| Affects | All nail swings + Nail Arts |
| Does not affect | Spells, Sharp Shadow, summons |
| Predecessor | Fragile Strength (600 Geo from Leg Eater) |
| Upgrade cost | 15,000 Geo (Divine) |
| Repair cost (Fragile) | 350 Geo per shatter (Leg Eater) |
| Break-even | ~40 deaths vs Unbreakable conversion |
| DLC | The Grimm Troupe (Divine availability) |
Per the wiki, the +50% boost matches Quick Slash's effective DPS uplift but applies the multiplier flat to every hit rather than scaling attack speed. The two stack multiplicatively for roughly 2.3x baseline nail DPS when paired; adding Mark of Pride brings the effective DPS to roughly 2.5x.
Both charms have the same +50% effect. Per the wiki, the only difference is shatter-on-death: Fragile breaks when the Knight dies and requires Leg Eater repair (350 Geo, or 280 Geo with Defender's Crest equipped for the discount); Unbreakable never breaks.
According to the wiki, the break-even math favours Unbreakable in long playthroughs. 15,000 Geo upgrade cost divided by 350 Geo per repair equals roughly 43 deaths before the Unbreakable pays for itself. Pantheon-of-Hallownest runs alone usually trigger 30+ deaths; Steel Soul saves cannot afford even one Fragile shatter, so the Unbreakable conversion is mandatory for those.
The wiki notes the visual tell. Fragile charms show a cracked-icon outline in the inventory; Unbreakable charms show a clean icon with no cracks. After Divine eats the Fragile and returns the Unbreakable, the inventory slot updates automatically; the charm's effect stays equipped across the conversion.
The conversion is a 5-step chain. Per the wiki, the Knight needs Fragile Strength first, then has to summon the Grimm Troupe via the Howling Cliffs Lantern, then trade with Divine in Dirtmouth.
Per the wiki, the 15,000 Geo cost is steep enough that most players save it for after the 31-Grub Grubfather milestone (1,500 Geo reward) and the Hallownest Seal/Wanderer's Journal sell-off via Lemm at the Resting Grounds shop. A clean run hits 15,000 Geo by the Crystal Peak clear without farming.
Unbreakable Strength is one of three charms in the canonical nail core trio. Per the wiki, Quick Slash and Mark of Pride round out the spine; Fury of the Fallen adds a panic-button low-HP damage layer.
Quick Slash pairingAccording to the wiki, Quick Slash + Unbreakable Strength stacks multiplicatively for roughly 2.3x nail DPS. The 54% speed boost combines with the 50% damage boost to produce the dominant nail-build core. Notch cost: 6 (3 + 3); the trio adds Mark of Pride for 9 notches.
Mark of Pride pairingPer the wiki, Mark of Pride extends reach by 25%; combined with Unbreakable Strength, the effective hitbox-to-damage ratio improves dramatically. Tight boss arenas like Markoth and Pantheon Watcher Knights reward the longer-reach damage stack significantly more than a Strength-only build.
Fury of the Fallen pairingThe wiki specifies Fury raises nail damage by 75% at 1 mask remaining. Combined with Unbreakable Strength, low-HP Pantheon runs hit roughly 2.5x base nail damage per swing. The combo turns near-death runs into clean kills; the trade is the 2-mask buffer the Knight needs to maintain at all other times.
The wiki notes an important anti-synergy. Unbreakable Strength does NOT affect Grubberfly's Elegy projectiles. Players running the full-HP projectile build get zero benefit from the +50% damage boost; the projectile damage stays at base tier.
The canonical 9-notch nail trio plus 2 sustain charms is the standard. Per the wiki, the build fits inside the 11-notch budget cleanly and dominates Pantheon-of-Hallownest first-time clears.
Unbreakable Strength (3 notches; +50% nail damage) Quick Slash (3 notches; +54% nail speed) Mark of Pride (3 notches; +25% reach)
Grubsong (1 notch; SOUL on damage taken)
Stalwart Shell (1 notch; longer i-frames)According to the wiki, this 11-notch loadout covers damage, speed, reach, sustain, and a defensive filler in one budget. In actual play, the loadout fits Pantheon Markoth, Pantheon Watcher Knights, and Pantheon Pure Vessel without overcharming; the trade is no spell-damage support, so the SOUL pool runs to Focus heals only.
Unbreakable Strength ties to the Grimm Troupe DLC, the Divine upgrade quest, and the canonical nail-build core. These spokes pick up the threads.
Game data and screenshots adapted from hollowknight.fandom.com, used under CC BY-SA 3.0. Original content remains the property of the wiki contributors and Team Cherry.