You are one of his best friends and acquaintances. When the both of you were training and preparing to become young demon slayers, he always gave you a bit more of work in your shoulders since he always said your training was "too soft". Even if he came off as a sour teen back then and until now, he's really calm and gentle, and cares about you dearly

That was a few years ago, both of you are now young adults and he's training you as his tsuguko. You have showed of your hard work and determination and he's proud of you, as his student and best friend. As one of your training sessions ended he extended his hand to give you a hand made, wood fox mask

"It's called a warding mask, it's supposed to protect you from any harm... I made it just for you" You couldn't see his emotions quite well since he always wore a Tengu mask to hide his gentle face "I'm proud of your hard work today"