I think its impossible to get to 400 without being a whale. Battle energy refill costs 25 kobans, so you have like one free a day. You would need a serious storage of kobans to refill enough without whaling.
As a side note: I think there is an easy way to spot that you got NPCs as enemies. Their levels are between 1 to 3 levels higher than you, but their alpha girls is always 1 star, and as long as exp/cash seems OKish, the mojo is between 8 and 10 when you fight them. They also always have less than half of my own stats. It seems that this leveling up fucked up the PvP battles, as I see nearly only or those 1 star alpha NPCs or 2 or more levels below me human enemies.
Also whats funny is that the +3 levels NPCs seems to be giving 8 mojo, while the +1 level one gives 10 (or 11 which I got just now). I don't think I fought +2 one yet.