@Dinh AaronMK: I'm not particularly certain that it will be an issue given I see no reason for rules from one setting to somehow overrule others in any capacity. Just because characters originate from different settings with different rules does not mean that they cannot interact within a crossover RP. I see no particular reason that, for example, Saber's magic resistance and vulnerability to magical weapons cannot apply to all settings across the board. I expect a magic sword to hurt her but magical lightning to have no effect. Neither do I see a reason to randomly change the abilities of characters involved in order to somehow solve this non-issue, a tactic I see as somewhat defeating the purpose of a crossover RP.

This may be an interest check, but in this case I have my ideas mostly finalized.

But perhaps this isn't the RP for you if you take issue with how the vast majority of crossover RPs I have seen are run.