Well if the game wants to earn money fairly easy here some tips,

Purchase 60 stamina storage for 2 euro's 1x > 60 stamina for 5 euro's second time > 80 stamina for 20 euro's third time. (total increase of 200)
and 2 "fight" stamina for 2 euro's > 2 for 5 euro's second time > 6 for 20 euro's third time. (total increase of 10)

so you've people who already gave money instead of playing for free. I mean whales can keep the game alive, but why not let people give a small donation for convenience.
Or do like unlimited ninja, step up for paying so that spending 5-10 euro's on harem heroes give you VIP 1 privileges that include increase stamina capacity, and x amount of free kobans per day


Then another tip is to make newer maps harder, instead of dollar blocks. Make people spend upgrading their characters instead of couple 100k like some oil. Now it's so easy for me that I don't need to upgrade my character which I did in world 2.

As for epic, remove green items please. If you're afraid people will get the girls easily, just add more epic armor pieces.

Add another upgrade for the harem girls (awakened or something like that). That require 10x more affection to upgrade and some minimum level exp like 30 or something so people don't get it too early in game.