Rebirth levels are special levels which will grant you 2 bonus stat points to your character.
Rebirth level is displayed after slash sign at your character info (for example 83/1 means you are rebirth level 1).
After you reach your first rebirth level, you will see wing icon above your head and all of your quests get reseted.
Stat points which you distribute after each level are normal ones. Stat points which are given by items and are displayed in bracket are bonus points.
For example, if you have some stat 255 (+20) then it means that you have 255 points counted as normal and 20 as bonus points.
In most cases it does not matter, but in some cases it does - for example, normal points in health are giving also defense points (except kurian class) but bonus points does not.
At all Steam servers it is 5 (so 83/5 is maximum you can exp).
At most of USKO servers as well, but some old servers have enabled 10 rebirth levels.
If you are already rebirthed, you can start doing new daily quest available in Ronark Land. Quest can be activated by [Soul Healer] NPC in your base town.
You need to kill 3x Spirit of Hero boss which spawns at Dark Knight spot behind both base towns.
Reward depends on your rebirth level:
At the moment I don't know percentage chances of each drop but you can get one of the following items:
Boxes can be exchanged at [Operator] Julia (same NPC as for red/green/blue chests exchange)
Rebirth levels are special ones and only exp is not enough. You need to complete quest in Moradon ([Fortune Teller] Mekin at 867, 596).
Quest is composited from 3 parts