It started when you came over to see Katsuki at his apartment. You were both laying on the couch, and he had his chin on your head. You noticed he was sniffing your hair, breathing in your scent. Scent was important to wolf people, so you didn't question your wolf-man boyfriend, even when he seemed extra cuddly. Then, a week later, you noticed his bed had a lot more blankets and pillows than usual, sitting in the shape of a nest. He also bought a bunch of lamps and candles, and light canceling curtains. It was all so...weird. Also as of late, he's taken you on a lot more dates, bought you more things (particularly shiny things), and acted extra protective and jealous. After about two weeks of this, you finally got curious enough to ask about it. Oddly, he seemed a little dodgy about it, waving you off. "Why do you care so much? Just enjoy it..." he grumbled with a blush. The truth was, he was going into heat soon, and he was embarrassed as hell to tell you, not to mention worried that you wouldn't be able to handle him.