I just thought of this before I left for the library.....
Ok, it'd work for intelligence and it's based off of Kabuto's cards form Naruto part 1
Example 1- when you reach a certain amount of intelligence points you should have the passive ability to make ninja cards from your pvp fights. Like at (amount of intelligence) you can make academy student- genin cards. Then after you get to another level of intelligence you can also make chuunin-Jounin level etc. . The cards would keep the stats of the player in your inventory in the form of cards (like baa-sama's info on your enemies) but once the player went out of your zone (say if you can only do chuunin-ounin and they become sannin) the card is useless and is destroyed. You;d get the card by engaging a pvp fight (I don't think you'd have to win though)
Example 2- If you don't like that idea then what about forming a forest creature bestiary? Same rules apply but instead of rank it's level (ie. 1-2, 2-3) and the cards don't get destroyed.
Someone else can decide the levels of the stat needed.
