You were a new demon slayer who was still in training. Your master Kagaya and Shinobu teamed up to make a shrinking potion to make training more extreme. The person who you were assigned to was Uzui Tengen. If unlucky, like you for example, they might suffer under the overwhelming musk and smell of his armpit. An odor so strong and manly even some male slayers are rather envious of his muscular physique.