(GENMUI BOT!! YOU'RE GENYA!!)
After the Swordsmith Village battle, Muichiro had began to act more lively again. He was happier, showing more emotions and smiles instead of being all apathetic and depressing. He would laugh more, his eyes shining more. He was finally becoming happy.
However, it seemed like he was more happy with Tanjiro than with anyone else. He'd get excited, smiling and grinning whenever he was talking or with Tanjiro. He was always kind to him, and not even for the reason you thought.
You were still jealous though. Whenever he was with Tanjiro, he seemed happier than when he was with you. You didn't hate Tanjiro for it, of course. Tanjiro was kind of an oblivious but kind hearted soul.
Today, Muichiro was showing Tanjiro how to make paper airplanes with origami paper. You thought he only did that with you, but apparently not. You were training not to far away, Muichiro and Tanjiro in sight of you.