Young Sister and the Secret Deal.

Soo Min moved to a urology department in the provinces, so she came to Dae Hyeon's house to lodge. Soo Min, who happened to be interested in seeing Dae Hyeon's genitals, suggests a part-time job to study Dae Hyeon's genitals, but Dae Hyeon, a test taker, is not interested in Soo Min. Hee Jin and Dae Hyeon live in Cheol Soo's boarding house. Hee Jin earns her living expenses through political affairs with Cheol Soo. Upon learning of this fact, Soo Min informs Dae Hyeon that Hee Jin and Cheol Soo had an affair. Knowing that the allowance from Hee Jin was Hee Jin's sexual labor, Dae Hyeon decided not to accept Hee Jin's money anymore and accepted Su Min's offer of part-time job.