I've had this idea for a while, achievements. This would not only be end game content but also early and mid.So far I've thought about 3 categories for achievements so far:
Monster hunting: Involves killing mobs long term
PVP: Involves claiming bountys and killing players (Yes we already have dailys but this would be long term, like killing a total of 1000 players in your account lifetime)
Player Advancement: Involves things such as becoming a genin, chunin, anbu, puppet brigade, etc.
This is a little sketch I made of how it could look.
Once you complete one achievement, you unlock its continuation (Larva extinction I, II, II, etc)
Rewards could range from XP, coupons, stat resets, daily resets, special clothing or even titles.