In the third season of Sweet Home, Hyun-su is able to kill Nam Sang-won with the help of an ally who was assumed dead.
Nam Sang-won, Yi-kyung’s fiancé, was the first person to undergo monsterization. He was known as MH1 and was experimented on by Dr. Lim.
Becoming a special infectee enabled Sang-won to take control of other bodies. He abandoned his own body and took control of Jung Ui-Myeong’s body.
Later, he possessed Sang-wook’s body, which turned out to be unsuitable for him, and realized that he needed a stronger body.
Sang-won finds an ideal body
Sang-won sees Yi-kyung at Bamseom Bureau near his original body. Yi-kyung, believing him to be dead, mourns his death.
Yi-kyung is pregnant with his child, and the baby suddenly starts growing in her womb the moment she comes across her fiancé’s body.
After witnessing Yi-su’s growth in the womb, Sang-won deduces that his child will grow much faster than human children.
Yi-kyung loses consciousness, and Sang-won takes the opportunity to plant a part of himself into his unborn child. Moments later, Yi-kyung gives birth to their daughter.
Their daughter, Seo Yi-su, is born a monster with special powers. She can communicate with monsters and even turn humans into monsters.
As Yi-kyung is not able to accept her daughter as she is, Yi-su abandons her and goes to live at the stadium, the only place she knows.
Meanwhile, Sang-won, who has been waiting for his daughter to grow, follows the part of him that he planted in her to find her. He manages to find Yi-su at the stadium.
Upon discovering her powers, he realizes that he can become even more powerful in her body. Sang-won now plans to take over her body.
Sang-won meets his end
Yi-kyung is turned back into a human by Hyun-su and follows her daughter to the stadium, where she finds out what Sang-won intends to do with Yi-su’s body.
She reconciles with Yi-su and tries to leave the stadium with her, but Sang-won catches them leaving. Yi-kyung then sacrifices her life to protect her daughter.
However, Yi-su fails to escape and is held captive by Sang-won. To be able to face her father, Yi-su turns several people into monsters to fight alongside her.
All her efforts to defeat her father fail, and Sang-won succeeds in taking over Yi-su’s body. Hyun-su, who does not want to hurt Yi-su’s body, then struggles to kill Sang-won.
Unlike Hyun-su, Eun-hyeok does not hesitate to harm Yi-su’s body. Yi-su manages to gain control of her body for a brief moment to prevent Sang-won from defending himself.
She allows herself to be stabbed by Eun-hyeok, forcing Sang-won to leave her dying body. Hyun-su and Eun-hyeok still find it hard to kill Sang-won, as he keeps possessing different bodies every time they land a fatal blow.
Eventually, Sang-won goes back to Sang-wook’s body. It is revealed that Sang-wook is still alive, which is why his body has been rebelling against Sang-won’s possession.
Sang-wook finally finds a way to kill Sang-won. He does not let Sang-won leave his body and walks into the fire, killing himself along with Sang-won.
Also Read: Ha-ni: Sweet Home character explained
