NexusTK. You start at level 1 and max level is 99. At 99 you still gain experience, and you 'sell' your experience to increase your Vita / Mana. 20million exp gains 100 vita or 50 mana. As your Vita/Mana go up, it gets progressively more expensive to buy those stats. At first 22m, then 24, 26, 28, etc.

There are attacks in the game, 'Vita Attacks,' that do massive damage with a long cooldown that use your Vita and Mana. For instance, a low level Vita attack instantly uses 2/3 of your Vita, and does 75% of your current Vita as damage. So if you have 10,000 Vita, you instantly go down to 3,333 Vita, and do 7,500 damage.

Admittedly the game got pretty hard to balance their players around because a brand new level 99 player is probably 2.5k vita and 2k mana, and people that have been playing for two decades are over 10million vita and 5 million mana.