Q
Does NIRA-CHAN (Haze Haseru Haterumade)
's "Attack +50 if your opponent's character's attack is 0" take effect when my opponent has no character card in their battle zone?
A
Yes, it does.
"Your opponent's character's attack is 0" includes their character card having 0 attack, and also any case where they can't attack so their attack is 0, such as not having set a character card or having set a character card without its power cost met.