Blood Type B, Wet and Hot Sister-in-law: Min Soo's younger brother Kyung Soo says he goes to sleep at Min Soo and Young Hee's house as usual. Due to Young Hee who is busy on business trip and Min Soo who went out for work Kyung Soo while being in the house alone suddenly meets Young Hee's younger sister Ga Hee, who suggests having a beer to resolve the awkward situation between the two of them. Ga Hee, who was drinking beer with Kyung Soo, gets drunk and somehow has sex with Kyung Soo. In fact, Ga Hee came when Min Soo was alone to seduce her brother-in-law.