Joon-soo learns that his friend Hee-gyu's sister Hee-jin has no where to go after being scammed, so he suggests living with him. The two start living together. They are close like brother and sister but they can never be that.
Mutual Relations
The Price We Pay
Demon Slayer: Kimetsu no Yaiba - Tsuzumi Mansion Arc
Shark Side of the Moon