Onii-chan wa Oshimai! Koushiki Anthology Comic - Vol. 6 Ch. 91 - Onii-chan is Done For Within the Closet Door

[KagamiGaSuki]

He was just marking his territory! He wasn't afraid, it's called scent marking!

Male cats stop spraying if you castrate them. So either Mahiro is not as done for yet, or this is an invalid excuse.