Chiemi's twin sister Natsuko is the real ousama, but Nobuaki does not realize it since he wished for the Ousama Game to never come about, because of this Chiemi was forced to switch places with her twin (in the new dimension his wish created) and thanks to that Natsuko wasn't angry at her father for abandoning her and her curse never comes about and thus remains dormant within her system.
Since in Ousama Game-Kigen it is implied that strong negative emotions are what trigger the virus to emerge, remember the scene (with the original Natsuko) where she was in the shed crying because her mother and the village were tormenting her due to the fact that she was in love with her own cousin?
That HUGE AMOUNT OF STRESS is what caused her immune system to weaken enough for the virus to enter her.
Consequently Nobuaki is unaware of this so he continues to go about his daily life and ask the twin Natsuko to be his girlfriend without knowing it's not Chiemi.
(NOTE THE PAUSE & THE EXPRESSION ON HER FACE BEFORE SHE TOLD HIM YES)
iN the end the virus will be laying in wait until a future generation triggers it to the point where another King's Game begins.