he seemed too shocked in c16 though, where he first puts two and two together for jy. which is why i think that he's investigating h100 'cause of smth that happened with his dad, the actual source of his nickname happy (c1). i just want everything with jy be a 'happy' just a coincidence 'cause i love it when chars have their own goals not revolving around the MC lololol. besides, his life in brazil seemed too hard for him to even think about an overseas idol he doesn't know (he only recently moved to korea)
Hey it could be both. The drug was originally made in Brazil and while he was living there something could've happened with his dad and that could be his motive for doing all of this. Jaeyoung could've learned the drug is now specifically trying to be mass distributed in Korea. But why Korea specifically? So he did research and learned about an incident in Korea with a famous boy band from years ago and decided to become a rapper to get his foot in the door. I think anything is possible and I like listening to all kids of theories.

I have a theory that our rapper Seungmin is actually a detective and has been trying to get to the root of the happy drug for a while now. I think he knew about Jaeyoung suffering from the drug as well and learned it was probably connected to the original group member Jun. So Seungmin decided he would come on the scene out of nowhere and quickly became a star in rapping. He did this to meet Jaeyoung and getting his attention in hopes of getting closer to learning more about Jun, who is in the upper ranks of distributing the happy drug. This would explain why he chose the exact same name "Happy" and instantly wanted to work him after only meeting him one time.
I don't think he expected to fall so hard for Jaeyoung, but as we all have seen, Seungmin has definitely fallen hard for him and so things just kind of happened in an unexpected way.