A younger brother living with his brother and his wife. One morning, when his sister-in-law tried to wake up the younger brother, she lifted the duvet, and the bulge in his crotch came into view! What is that? Could it be... this is a morning erection? Unlike men, the sister-in-law who doesn't know about morning erections can't stop her heart pounding at the shocking bulge in her crotch! I saw something I shouldn't have... That sense of immorality gradually changes into lewd emotions, and before she knows it, she's sucking his cock through his pants! Please! Don't wake up! she thinks while engrossed in fellatio. The younger brother, who finally felt a strange sensation in his crotch, woke up and was surprised! But seeing his sister-in-law's lustful expression for the first time, his rationality flew away, and he suddenly collapsed into sex. No one is at fault. It's just that the morning erection destroyed the rationality of the two.