Website and data research by 101Leafy.

101Leafy researched how the game works out damage. Pick who attacks, who takes the hit, the action, and the moon phase, and the calculator follows the game's own steps, rounding down after every division.

Almighty skills are left out, since their affinity is not worked out yet. Demons fill in their own stats; for the hero and partners, enter the stats from the status screen and add up the defense of every piece of armor.

How damage is worked out

1. Battle stats: weapon attack Lv/4 + St + weapon power, gun attack gun power + bullet power + Lv/4, normal attack and physical skills (Lv + St) x 2, magic attack In/4 + Ma. Defense is (Lv + Vi) x 2 for demons and armor + Ag + Vi for humans.
2. Buffs: a value with a buff of n becomes x * t / 8, with t = 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16 for n from -4 to 7. Poison halves attack after the buff.
3. Physical: q = attack x (attack/4 + 4), at most 65535, then d = q / defense, with defense at most 255. Physical skills then add d x power / 100.
4. Magic: md = the target's magic attack + its defense / 4, at most 255, then d = 2 x (magic attack x power / md).
5. Moon: d x T / 16, with T from the attacker's moon type and the phase. Humans always use 16.
6. Criticals, physical only: v = 2 x P + 2 x Lu + Ag, plus 8 x the demon's critical value, with P the phase for the party and 8 minus the phase for enemies. A random number from 0 to 255 below v means no critical; otherwise a second one below 4 gives x3 and below 16 gives x2. Luna Blade at the full moon and Sol Blade at the new moon skip v and roll 0 to 63, so 1 hit in 4 is critical.
7. Defending halves the damage, and affinity follows: x5/8 takes 5/8 of it, x2.5 two and a half times. A reflect or drain half takes half.
8. Spread: d - d x r / 128, with r a random number from 0 to 31, so up to 24% off.
9. Hit for weapons, guns, and normal attacks: x = target evasion + 16 - hit, with evasion Lv/2 + Lv + Ag + (In + Lu)/4. Below 0 it always hits; otherwise x squared / 32 + 1 of 256 rolls miss. Skills and spells: e = 2 x (2 x target In - hit + 16); 255 and up, or below 0, always hits, otherwise e + 1 of 256 rolls miss.