Let me add a little more :
"Apostolia sistem is unlocked after reaching ep3 of story"
An ep or episode acts as a season of the game main story trough wich you go traveling between worlds , here is an example:
Ep1 :iruna & dark domain
Ep2 :dragon's world(forgot name) & xeltzam world (same)
Ep3 : mysterious world resembling iruna with a different turn of events.
After defeating irai ,the first boss of ep3, you unlock the "apostolia" system this system lets you
1)train stats = allows you to break the cap of points in a stat (256) by giving half the exp u get to a stat during training
Ex:"started training vit"
You got 150k exp , normal was 300k , 150k goes to stat and 150k to your lvl.
A stat takes 5 times more exp to lvl than players.
2)ignite : system wich grants a power-up dependant on type of weapon , starts at a 30 secs duration then gets 1 extra after each 2 uses , during an ignition stat training needs same exp as normal player to lvl up.
3)ai christa : system that grants player 5 slots for special xtall known as ai ,
These xtalls have colour and by combining them in lines you get special effects
Ex = red vit on mid + green str on top grants a yellow line (atk and melee penetration).
4)extra stats ,unlocked in apostolia menu =
Igt : raises ignition duration
Igr : speeds up ignition recharge
Exp : exp obtained +0,5% for point (1% during ignition)
Blue : raise effect of blue lines
Red : raise effect of red lines
Green : raise effect of green lines.
Note = raising 3 stat lvls grant 1 stat point for expending.
Sorry it got so long but they all are related