This is going to come out as a stupid question, but like they say in southpark, there are no stupid questions, just stupid people.
I just pulled Gamma Bomb and it says to KO all Characters, this I assume means not only your opponents but also your own characters? With a direct KO, your opponent loses endurance equal to the recruitment costs, but do you also lose endurance. And do you KO stunned and exhausted figs as well, and further does your opponent lose endurance on those as well, thereby potentially losing endurance twice in the same round on the same character. Thanks in advance.

I can't find anywhere in the rulebook where it says you lose endurance equal to the recruitment cost when a character is KO'd. It says that for when a character is stunned. there's a difference between stunned and KO'd.
So gamma bomb does not cause any endurance loss. It just KO's all characters in play(sends all characters to the KO'd pile)...wether they are exhausted, readied or stunned.