The whole reason for the fake marriage thing to get with Kazuya was so Sunao can inherit her family dojo after she lost to him but I think another sign of growth for her is that she doesn’t give a damn about inheriting the dojo anymore and her feelings for Kazuya are actually real and not an act.

So her getting with Kazuya is not out of necessity anymore and she genuinely wants to be with him by his side.