Hero: I shot you!
Villain: Nuh uh, I had my barrier up!
Hero: You didn't say you had a barrier until after I shot you. You're out!
Villain: Nuh uh!
Hero: Uh huh!
proceeds to slap fight
It was certainly implied when it took over all the other kaiju and #8 was all, "We've always been at war with this specific kaiju" flashback.
The second half of this series certainly went off the rails real quick.