That picture they sent to his gramps was surprisingly cute. Yuzuru isn't a spineless protagonist, and I don't think his family can be taken lightly either. This wannabe playboy picked the wrong girl to try and pick up and the wrong guy to mess with. Even then, I think they can also use the "we're already engaged" card against this creep. Or maybe at least that "couple" pic can come in handy. They're far from helpless in this situation.