In reality, the NORKS have close to 5000 artillery pieces already in place with known locations to shoot at in the city, and around 1000 Migs than can reach Seoul in a minute or so after launch. Not counting the tanks and APC's ready to break out of underground tunnels under or over the DMZ. Its a tenuous situation to say the least with Seoul having a population of 25.6 million people (almost half of the total country's population) located in an area where a concerted attack of conventional weapons could kill hundreds of thousands within days.Following you. It is my understanding the Japan moving in a huge fleet is something new.
All of that said, I still don't think the pillsbury fat boy is ready to die for his country. It is a chip in their box though in negotiations.