My sister, who always wears my clothes without permission, is wearing my shirt again... and then I glanced at her again and realized she wasn't wearing a bra! HUNTB-512

My younger sister always wears my clothes without permission. She's short, unlike me, who's quite tall. The second time I couldn't help but look, I noticed she wasn't wearing a bra or pants; her underwear was completely exposed. Shocked by what I'd seen, I got an erection. Noticing the abnormality in her lower body, my sister suddenly became shy and effeminate. Now, feeling each other's sexual attraction, the atmosphere suddenly turned erotic, and we finally crossed the line of taboo.