Idea: For every time you gain a level on one character, you additionally gain a page of knowledge.
This page of knowledge is account bound, has a maximum level requirement equivalent to the new level of the character and can be used by any character that does not exceed the level of the scroll of knowledge.
(i.e. a page generated by a character that levelled to Level 10 cannot be used on a Level 80 character, but used on a Level 10 or lower character)
Upon using the page, the character that uses this scroll gains 5% of XP needed for the next level.