they went to stop china crisis by stopping the trickster, china's number 1 hunter, for a korean nacional mission but it happens he is involved with the criminal organization where kiddo, USA number 2 hunter, is the leader in disguise. They want to let china's tower destroy the country (and probably take over) and Jiwoo, the queen, just prevented that.
She went there just because she wants to protect ji-rok, her brother. The plot twist is that Kiddo predicted that and the actual purpose they're trying to wreck China, is so that Jiwoo aka the strongest hunter in the world gets away from her country so that he can destroy Korea while she's away. The thing is, she had predicted someone would try funny things while she's away, so she left some instructions to the people there.
Right now, where at the part where jiwoo kills trickster. We still don't know what is happening in Korea, will see in the next chapters probably.
A little correction to your reply
Jio and jirok went to find the person who is impersonating their grandfather "trickster" who is part of the terrorist group, the liberators (kiddo is the leader btw). But this is a trap by kiddo because while jio is in China he's going to cause trouble in korea but obviously jio already knew this so she set someone to be there while she's away. Anyways when they were in China they found out there's a small civil war and china no.1 (one of jio acqataince) was branded as traitor because he was helping out his friends in the demonic sect and had to went into hiding. But since he has the eyes of truth that can see lies, he is the only person who can prove that the trickster is not jio's grandfather. So jio has to go run some errands for him and mend his relationship with his sister in exchange for helping her prove to the media that the trickster is a fraud.
The translation is so ass so I understand why people find the story is confusing honestly. (▰˘◡˘▰)

chat in ngl i’m a little confused on what’s going on in the current timeline….