Its not based on the charm counter, it's based on the suspicion counter (see fanmade guide on how it works). 

But if you dont wanna look at the fan made guide, then here's a short explanation:

Do the neutral route but side with the bulls most of the time. Show Axel the spy's heart, lead his army when you scare away both tribes with the fear potion, and give the bulls the fruits (you still have to sabotage the bomb and the rogue lizards' test).

Fair warning: saving the lizards from being hanged will essentially lock you out of Nauxus's sex scene (since he wont trust you as much).