DEF and RES reduce damage in different ways
An attacker’s stats do not determine damage alone. The target also has defenses. DEF feeds the defense part of ordinary damage calculation. RES is resistance to the relevant damage Element. Lowering one does not automatically lower the other.
This guide separates effects that change those defenses from effects that bypass them for particular damage. Its numerical example isolates ordinary elemental resistance; it is not a complete formula for every damage family or encounter.
Also separate Elemental RES from Effect RES. The former concerns damage. The latter concerns whether susceptible effects are applied. Increasing RES PEN does not make a base-chance debuff more likely to land.
Reduction changes the target; Ignore qualifies the hit
DEF reduction lowers the enemy’s DEF while the effect is active. Pela’s Exposed is a clear example: her Ultimate attempts to apply a status that reduces enemy DEF. Damage that uses that enemy’s DEF can benefit during the effect.
DEF Ignore tells qualifying damage to disregard some of the target’s DEF. It does not mean the target now has a matching DEF-reduction debuff for everyone. The qualifying attacker and damage type matter.
Scroll horizontally to see all columns.
| Effect | What changes | What to check |
|---|---|---|
| DEF reduction | The target’s DEF | Application, duration and affected targets |
| DEF Ignore | DEF counted for qualifying damage | Whose damage and which attack types qualify |
| RES reduction | The target’s relevant resistance | Element, application and duration |
| RES PEN | Resistance counted for qualifying damage | Element and recipient of the penetration effect |
For example, the Light Cone Baptism of Pure Thought grants its wearer Disputation after using an Ultimate to attack an enemy. Its DEF Ignore applies to the wearer’s follow-up attacks while that effect lasts. It does not grant every teammate unconditional DEF Ignore.
Qualifying DEF effects add together
In the ordinary DEF model, applicable DEF reduction and DEF Ignore combine additively for a qualifying hit. Suppose a target has 30% DEF reduction and that hit has 20% DEF Ignore. The combined amount is 50%, leaving half the target’s otherwise applicable DEF counted for that hit. It is not two successive discounts leaving 70% × 80% = 56%.
That does not mean the hit gains 50% damage. DEF is an input to its own damage multiplier, and the resulting gain also depends on the existing defense situation. A DEF percentage and a final damage percentage are different quantities.
The Genius of Brilliant Stars set gives a concrete wording example: its four-piece effect ignores 10% DEF, plus another 10% against an enemy with Quantum Weakness. The additional condition matters. A set bonus that limits Ignore to a special damage family must likewise stay within that family.
The 30% and 20% above are assumed active values, not a suggested team. Do not count an expired effect, an ineligible hit or a duplicate effect whose description forbids stacking. This example does not establish over-cap behavior.
RES PEN addresses the other defense
RES PEN reduces the relevant resistance counted for the damage it affects. Element-specific penetration applies to that Element; All-Type RES PEN is not restricted to one Element. Neither is another name for DEF Ignore.
Read the effect’s recipient
Ruan Mei’s Ultimate creates a Zone that grants allies All-Type RES PEN.
The penetration is an ally benefit while the Zone applies. Her Ultimate also describes other mechanics, which should not be folded into that RES PEN percentage. See Ruan Mei’s Kit for the complete conditions.
Twenty points of penetration need not mean 20% more damage
Consider an ordinary hit with 1,000 damage before its resistance multiplier, with every other factor already held constant. Assume the enemy has 30% relevant RES and no RES reduction. Using RES multiplier = 1 − effective RES, the result is 1,000 × 0.7 = 700.
Now apply 20% relevant RES PEN. Effective RES becomes 30% − 20% = 10%, giving 1,000 × 0.9 = 900. The increase from 700 to 900 is about 28.6%, despite penetration increasing by 20 percentage points.
These are hypothetical positive-resistance inputs, not an enemy database or a rule about resistance limits. Read 30% as 0.3 when calculating. A Weakness icon alone is not enough to supply the exact resistance value for every encounter.
An effect must be active when the damage happens
Before comparing percentages, check whether the effect reached the right target and covers the right attacker. Pela’s Exposed uses a base-chance application; that is a separate question from how much DEF it reduces after landing. The Buffs and Debuffs guide explains application, duration and removal.
An effect restricted to follow-up attacks cannot be counted for every Ultimate merely because the Character uses both. Nor does a debuff on one enemy improve the same attack against every other enemy. Track coverage before adding values.
Keep the comparison controlled
Compare the same damage source against the same target, with matching buffs and combat conditions. Do not add DEF reduction and RES PEN into one percentage: they affect different parts of the calculation.
If an effect instead says it increases damage dealt or damage received, continue with DMG Bonus and vulnerability. Identifying the correct family comes before deciding which support effect is useful.