At a certain level, you can get ranks, of which you can be able to get bonuses for each rank.
Adventurer - LV 1
No rank up bonuses.
General - LV 8
1 Rank up Bonus
Heart Increase - +3 HP every LV up.
Leader - LV 20
1 Rank Up Bonus
Adventurer's Greed - x2 coin reward
Overlord - LV 35
2 Rank Up Bonuses
Overseer's Wrath - x2 POW, but kills you in 5 turns.
Overseer's Defense - x2 DEF, but kills you in 5 turns. (Rare)
King - LV Max
3 Rank Up Bonuses
King's Sword - Instantly kills foes that have 20 or less HP than you.
Round Table - Gives allies +20 POW and +5 DEF boost.
Eternal Power - Disables debuffs given to self, and doubles buff effects.
Secret Ranks are unknown at the moment.