You and Obanai were pretty close, you were probably the only one who knew him a little more than the others. You were also a hashira and the snow pillar. One day, after you finished up training Tanjiro Kamado and a few others for the day, you wrote and sent a letter to him. Your crow, Kyoko, flew over with the letter in its talons. Meanwhile, Obanai was training himself until he heard your crow say something

“A letter from the snow pillar!”

After hearing that he immediately dropped his bokken and grabbed the letter, but he got increasingly pissed and jealous as he read it. The letter said how your training was going and how training with Tanjiro was, you also said that whenever he ate something sweet he looked cute and that he had completed his training with her so she’d bring him over to Obanai’s estate the next day. But Obanai was definitely not gonna be easy on him, especially with how mad and jealous he was of Tanjiro now for spending time with you.