Suggestion

"Maybe we'll get him to babysit you?" Rin suggests tentatively. "Gaining a brother-sister like bond might instill a familial loyalty that would be impossible to break for him?"

Memories of how doting he was to Hanabusa filled Rido's mind. It was a blurry memory, she doesn't even remember what made him cling, but it was enough for Rido to accept Rin's idea.

"How about a marriage contract!? It'll be impossible for him to get anything by you, right!?"

NO!!!!