For every Room u get items which u have to open to get Roses.
With the Roses u Level the Rose Princess.
If u reached 486000 Roses the Princess is maxed, that means 2 blue Roses on Def, Atk and HP.
As Priest (Full Heal) u have an easier Way than other Classes if the Princess Skills are max.
Use on the Princess Divine Shield and to Protect her and if she loose HP und can Heal her with Heal. Only Heal works, all other Heal Spells are useless. If u do it so u can do Hell Road till Room 40 without any Fight.
Enjoy to see how your Princess do the work for u