Let us level jutsu by spending blank scrolls on it (all numbers are random, it's just an example) :
For example 1 blank scroll from level 1 jutsu to level 2 jutsu will give us 3% of xp. If the jutsu require more xp like for example water prison, the cost of upgrade will be 1 blank for 0.5%.
From level 2 to level 3 will give 2% of xp, or as said before for water prison that requires more xp 0.25% per blank.
This will make the economy of the game better and will make the market of blank scrolls more viable in every time of the game.