Quote Originally Posted by sanahtlig View Post
The JP wiki says the bonus from the assist skill is 8%.

Also, every indication I've seen is that assist skills only affect the soul/kamihime that has the skill (a comment on the JP wiki affirms this). Moreover, I tested skill damage just now with Rosenkreutz vs. Mordred (no buffs or debuffs applied) under controlled conditions, and allies of Rosenkreutz did not do more skill damage.
Should that be reported as a bug, then? The English wiki explicitly says that Assist abilities are supposed to affect the whole team:

Assist (Passive) skills - These are active from level one, and affects the entire party's abilities when the Heroic Spirit is active. These do not increase in strength with level.