By defeating certain enemies in the game, you can raise the Level cap. Initially, you cannot proceed any further beyond Level 70, but you can extend it three times: to Levels 80, 90, and then 99. The three foes you must beat are available in the late-game through series of requests.

Unlockable	How to unlock
Boosted Level cap	Defeat the Great Dragon.
Boosted Level cap	Defeat the Blizzard King.
Boosted Level cap	Defeat the Storm Emperor.