@zeroxjac
Right, see this is the thing. With the Milena party he did the same thing, as you say, and then they became good friends. But it should have made that party EXTREMELY distrustful of him! Like he literally threatened to kill them if they refused the contract. I understand why HE might feel chummy toward THEM, but THEY should definitely consider him an evil person.
Like imagine that Superman and Jimmy Olsen are trapped in an airplane that's about to crash and Superman is like "okay now Jimmy, I can save us, but I'll have to reveal a secret. You have to keep this secret. If you tell anyone, I'll rip your head off. If you don't agree to my terms, I'll let this plane crash and you'll die." That's basically precisely what Rei did. That is not being nice. He could have just said "hey look, my griffon is rare and has special abilities. on your honor, please swear not to tell anyone" and they would have. He didn't even NEED to do the contract with the group.
And then what's worse is that he then accepts to do the contract LATER, after he shows them, defeating the purpose of asking for the contract at all. "You have to swear a contract of secrecy before I show you this, because I can't trust your word." "Okay, well let's wait until later to do the contract and show me your secret first." "Okay, that sounds good, I'll trust your word on that."