I think you guys are overestimating how much Kaido cares for Yamato. He placed cuffs on her that would have killed her:
However much he loves her, it's not to the extent that he wouldn't kill her if she disobeys him.
However much he loves her, it's not to the extent that he wouldn't kill her if she disobeys him.
She already disobeyed him by the way and confronted him, he beat the shit out of her but somehow I expect him to care about her and I expect her to care about him, both in their own special way (whether it's good or bad).
We will surely get a short flashback about their past and hopefully we'll also see Yamato's mother.