Continue west from Route 17 until you see the beach to your west. When you do, head south first to a small beach there containing the item PP Max , as well as a Prism Scale hidden to its south. Once both are in your possession, move back onto the water and head back north.
When you see that beach to your west once more, move onto it. First find the hidden Pearl near the shore, then move north-west over to the Battle Girl there. Final battle of the route!
Trainer Battle: Battle Girl
Once she's defeated, head north up the stairs into the Dark Grass. Grab the Iron here, then turn on your Dowsing MCHN and head west. Use it to find the PP Max hidden here. And that's everything in south-east Unova!
If you haven't explore east Unova (starting at Undella Town ) or west Unova (via Clay Tunnel ) yet, we'd recommend doing so now! More post-game areas to explore! Feel free to look at any other post-game content or anything that takes your fancy though!