Responses
I don't believe Zai is stupid, it takes a smart demon to decide not to fight after all if he does not know why he is fighting why should he. And I don't believe his Master is manipulating him, he genuinely loves him. He shows it differently but that is love between master and demon.
Zai is demon and have a big body but become uke, he is good at fighting and sing but little stupid. The weapon merchant is easy to manipulate him. Did Zai never done that with another demon ? so this is his first experience with human. Loved it.