Hrm, the helpfile might be a little misleading. This bonus, which I believe you mean, is:
Intelligence is an important factor in learning between combatants. If
a character fights a creature several times, the more intelligent of the
two opponents will gain an advantage over time...
This bonus is purely PvE not PvP. I suppose it might be able to be extended to PvP with some work, but I'm not sure that is super cool. However, the helpfile might need to be cleaned up, especially since it uses the word 'jutsus' which is a typo. The only thing I think I thought, wow that is an exciting phrase, is by using the word 'creature' it would imply NPC without spelling it out in gory detail.