Officially Dating: The Do Family Head keeps trying to set Kyunwoo up with a Swordsmanship System daughter from another family. He needs to be "officially" dating her because Haneul is not appropriate for his status and dating rumors can wreck his reputation. This brings an endless amount of anxiety to Haneul. Kyunwoo doesn't want to make Haneul official because the torment his mother endured is always on his mind and he doesn't want to put Haneul through that. Things come to a head when Haneul is so upset that she basically asks if they'll wind up doing
everything together except date to which Kyunwoo cannot even respond.
Eventually he takes the words of another Ain to heart and asks her out formally in a private confession with a gift of necklace and flowers under The World Tree. Also, to reciprocate Haneul offering him her tail, he offers her his neck as the most vulnerable part of the body.
Marriage: The Do Family Head doesn't mind Kyunwoo dating Haneul if it's to learn how to interact with women. However, he draws the line at marriage. He can take Haneul as a mistress but his legal wife cannot be an Ain. If Kyunwoo fails to abide by this, he will be expelled. Kyunwoo is so angered by this he goes straight to Hanbyul's love interest and commissions a wedding ring on the spot with materials he has on hand. He then runs over to Haneul and proposes marriage and this is when Haneul's mental health is totally healed (she no longer feels insecure or jealous). The ring he made has a small ruby the color of her eyes. It's a color she hated so much but Kyunwoo loves it and she realizes the meaning behind it. He makes it clear that he knows the road ahead won't be easy, but he promises to face everything with her together. Kyunwoo then bundles everything he ever received related to the Do Family and ships it to the family head alongside a copy of their marriage certificate.