Not all of the pieces are in the puzzle yet. It helps to read this all in one go though, so I reccomend finding the novel. I feel like the comic kinda cuts parts out that make extra difficult to understand. The most important take away is: They were both in Mexico, JHan(ML) was a soldier who escaped in a hazmat suit, Guk saved a guy in a hazmat suit and wants to kill him for not saying thanks and running away.
The political stuff is mostly US asked Korea for help and planned to pin the blame on them after also using them to kill innocents. They fabricated a situation using the Heartless threat as motive. JHan was part of that Korean squad. And Guk just literally happened to be there. Purely, absolutely, by chance. So the reason he's connected at all to the supplier or anything related? Pure chance.
There will be more info to come though, it'll become more clear. Promise.