Changes from Suikoden III
1. In Suikoden III, it was possible for characters to attack on the same turn they cast Magic Sword, but there is no chance for that happening in this game; you must always use a turn to cast the buff.
2. In Suikoden III, the only way to increase damage from the Magic Sword state is to learn and use the Sword of Magic skill. In this game, both skills and the elemental affinity can boost the Magic Sword's damage multiplier.
3. In this game there are 2 versions of the Magic Sword spell: a level 1 (named like "Sword of Cyclone") and level 3 spell (named like "True Cyclone"); the Level 3 provides a higher physical damage multiplier, so you will always want to cast the level 3 spell.
4. in this game, the Sword of Magic state does affect command attacks and counter/"thrust-back" damage just like boost/double-edge (while in Suikoden III it did not). i'm assuming it helps in unites too (not fully tested, but it's been verified unites factor in the critical hit and multiple-hit mechanics as well).
Soooo, I just did some numbercrnching with the spreadsheet, and I think I've worked it out...
Basically, the sword spells add a multiplier (1.1 and 1.2 for the first and third level spells), then SoM and it's epic counterparts add another multiplier. In the case of two SoM skills, it adds a multiplier for each skill (2 total). It looks like the multipliers are as follows:
Level - Normal / Epic
E - 1.05(*) / 1.02
D - 1.08 / 1.05
C - 1.12 / 1.08
B - 1.15 / 1.10
A - 1.18 / 1.12
S - 1.20 / 1.15
SS - 1.30 / 1.20
It also includes a multiplier for the elemental affinity corresponding to the spell. I've used the following values for these...
Affinity Level - Multiplier
E - 0
D - 0.5
C - 1
B - 1.1
A - 1.2
S - 1.5
...which I got from the results with no skills. This gives a final calculation of:
Damage = Base * Spell * Affinity * Skill (* Skill 2)
For example, Kyle with both Sword of Magic and Zen Sword equipped and at SS would do 1 * 1.2 * 1.5 * 1.3 * 1.2 for about 280% (2.808) of his normal damage
Royal Paradise, Sacred Oath, and even Zen Sword improve the effect of the magic sword. thus the description for Zen Sword in the game is inaccurate.
other things to note
1. if you cast the lvl 1 then the lvl 3, it will do the lvl 3 effect/damage. if you cast another lvl 1, it will revert back to lvl 1 effect/dmg... don't waste your time switching in 1 battle!
2. Having an E affinity in the element your Magic Sword is using will result in dealing 0 damage!