The assigned combatant's attack cards with a cost of 1 or less deal +10(20)% damage.
When the assigned combatant uses a Skill card, +10(20)% attack card damage for 1 turn. Stacks up to 3 times.
Light of Judgment (3 EP):
Deal 100% Damage to all enemies. Draw 1 Attack card(s) from the assigned combatant with cost of less than or equal to 1.
At max stacks, she provides a staggering +80% Generic Additive Multiplier (20% base + 60% from 3 skill uses). For a 100% base card, this nearly doubles your card multiplier instantly. Because you assume max uptime and skill usage, she mathematically brute-forces her way to the top for 1-cost cards.
2) 5★ Scarlet (ME0)
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If a card used immediately before was from the assigned combatant, +15(30)% attack card damage. Stacks up to 2 times and is removed if another combatant's card is used.
When the assigned combatant uses 2 or more cards, they gain [Focus].
[Focus]: Attack card damage of the assigned combatant is increased by 20(40)%.
Remove [Focus] when another combatant's card is used.
Binding Knot (3 EP):
Deal 250% Damage. +10% assigned combatant's attack card damage for each owned buff for 1 turn.
Scarlet provides a +50% Generic Additive Multiplier (15% x 2 + 20% Focus). While she is extremely powerful for a "Yuki-only" spam turn, she is eclipsed by Lilian at ME4. Her main advantage is that her buff is slightly easier to maintain in shorter rotations compared to stacking three skills.
3) 5★ Westmacott(ME0)
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Attack Cards of the assigned Combatant drawn through that Combatant's ability gain +25(50)% Damage Amount for 1 turn.
Increases Damage Amount of the assigned Combatant's cards that have Inspiration by 10(20)%.
Clue Spotted (3 EP):
Move 1 card from hand to Draw Pile. Draw 1 assigned Combatant card.
She is the only partner on this list who occupies the Generic Card Multiplicative Multiplier slot. Her +35% Damage Amount (25% draw + 10% Inspiration) scales your entire (Base + Potential) block. While the raw number is lower than Scarlet or Lilian, she is the "endgame" choice once your additive multipliers are saturated by other buffs.
4) 4★ Lilian(ME0)
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The assigned combatant's attack cards with a cost of 1 or less deal +10(20)% damage.
When the assigned combatant uses a Skill card, +10(20)% attack card damage for 1 turn. Stacks up to 3 times.
Light of Judgment (3 EP):
Deal 100% Damage to all enemies. Draw 1 Attack card(s) from the assigned combatant with cost of less than or equal to 1.
Even at ME0, she provides a very solid +40% Generic Additive Multiplier. She functions as a "Budget Scarlet," providing high consistency for 1-cost cards, though she lacks the explosive top-end scaling of her ME4 version or the 5★ alternatives.
5) 3★ Douglas (ME4)
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The assigned combatant's Attack is increased by 8(16)%.
At the start of battle, Damage dealt by the assigned combatant increases by 8(16)% for 1 turn.
Giant Bazooka (2 EP):
Deal 120% Damage to all enemies.
Douglas is the only partner here boosting Final ATK (+16%). While this helps hit Potential Node breakpoints, his additive damage (+16%) is significantly lower than the others. He is ranked last because, at max uptime, the massive card multiplier gains from the specialized partners far outweigh a small Attack boost.