After you meet up with Kieran at the Kitakami Hall signboard, you go through Oni Mountain to visit the ogre's den.
Explore Oni Mountain
If you go northwest from the paved path, to the northern part of the area, you can find a TM043 Fling.
You can optionally go northeast from there across the mountains to find a TM001 Take Down on one of the small grassy areas northwest of Kitakami Hall, a TM045 Venoshock on the grassy area just north of Kitakami Hall, and a TM163 Hyper Beam northeast of that on a grassy area north and slightly east of Kitakami Hall.
North of the river in this area, there is an eastern cave where you can find Hoothoot and Cleffa, and you can find a TM035 Mud Shot.
There is a cave west of that with a TM086 Rock Slide in front of it.
Go back to the river and go south to the area west of Kitakami Hall. Go to the southwest end of the dirt path and you can battle Hiker Miyu, who has a level 59 Hisuian Sandshrew and a level 61 Hisuian Vulpix. You get 3660 Pokédollars for winning.
Northwest of Hiker Miyu, you can find a TM008 Fire Fang.
South of Hiker Miyu, you can find a TM047 Endure behind a spire of rock.
Go southwest from Hiker Miyu to find a small bridge over the river. Cross it, then go southwest from it and you can find a TM009 Thunder Fang.
West of the bridge, you can find a TM183 Super Fang.
Northwest of that, you can find a TM059 Zen Headbutt.
The path leads to a small waterfall. North of it, you can find a TM108 Crunch.
North of the TM, there is a cave where you can find TM191 Uproar.
Back outside, go south until you can go west. You will eventually reach a sign in the road. Before you continue, you might want to go left where it says to go to Infernal Pass, and check on the small sign nearby to add it to your map as a Fly destination. Then go back to the large road sign and go right to continue on the path to the Dreaded Den. The path goes near another waterfall, and southeast of the waterfall you can find a TM125 Flamethrower.
Keep going east and you will reach the Dreaded Den. Approach Kieran and there will be a cutscene. He asks if you want to battle. If you do, he will heal up your teams first. He has a level 62 Furret, a level 62 Yanma, and a level 66 Poliwhirl. You get 2904 Pokédollars for winning.
Afterward, there will be a cutscene. It will now be evening. Go back to the Community Center in Mossui Town, heal up, then go to the destination on the map, northwest of the Community Center. There will be a cutscene. You will get the Teal Style Card, which adds more clothing and hairstyles to certain shops. You won't be able to get other colors of jinbei until later in the game, however.
Go to the shed and approach Kieran and Carmine, and there will be a cutscene. Carmine challenges you to a battle. She has a level 62 Morpeko, a level 63 Mightyena, a level 64 Sinistcha, and a level 63 Swadloon. You get 3584 Pokédollars for winning.
Afterward, when you're ready to move on, go to Kitakami Hall, where you can join the Festival of Masks.