Perhaps something for both F2P and P2W players. Have level gaps for corresponding events taking place. For those level 30 and below can have nice events that'll help them get items and coupons to catch up and increase their strength, while also pitching them a decently strong ninja.
Players above 30 can have slightly more benefits, but not that above lower levels to they don't feel cheated.
This can be more focused around ninja fragments and ninjas they should be able to get.
And for the sake of a long strength, lower levels can be given the Chunin Medal, like it's given when they first start. And higher levels can be given and bare with me very limited Jounin medal as a trail.
It can of course be given without the coupons and naruto nine-tail fragment that comes with it.