The first chapter is actually a side chapter, but I'm calling it Chapter 28 since I'm continuing XLG's numbering method for this series. The second is another extra case. I think this is more of a break in the arc rather than the beginning of a new arc.
From what I can tell, neither of these has much to do with the main story. Chapter 28 has another bath scene, but you'll have to wait for Volume 6 to see the good stuff. Unless this series goes on an unexpected hiatus, I would expect that to be out in January.
Maken-Ki! is coming soon.