From what's been translated, the king of the landlocked country hasn't made an official appearance yet...but it's been hinted that he's just as shady as his children are.
The landlocked country does make an official apology and the other countries lift their embargo on their magic stones as promised, but the councilmen mention that the apology didn't feel genuine, rather, it felt like they were just saying it because they didn't care whether the trade re-opened or not. Even though the landlocked country continues to buy magic stones from the other countries, the council feels that their need doesn't feel as urgent as it was in the past, so it makes them suspicious.
During all that, Maki and Chiharu discover that they can "cleanse" the monsters (like the gazer in this chapter) that spawn from the miasma. They realize that they can communicate with some of them and find out that the monsters are attracted to the saints because they have the power to cleanse them. The most recent chapter I read, Maki and Chiharu find out that the monsters that are emerging are not ones that are usually found in the area and they have their suspicions that the monsters are coming from the landlocked country in some way.
I think the landlocked country are conducting experiments to produce monsters from the miasma so they can extract magic stones from them in some way...possible amassing them to declare war on the other countries, seeing how hostile they are to them.