Sorcerous Stabber Orphen: The Wayward Journey Volume 4 by Yoshinobu Akita

Leaving Kink Hall Village behind them, Orphen and his companions find themselves now in Fenrir’s Forest, the large sea of trees covering one fifth of the Continent. Few men ever set foot in this sacred land which the Deep Dragons have made their home. But something strange is afoot in the Dragons’ Valhalla. It’s there that Majic meets a young girl called Fiena who wields a mysterious power linked to the Forest itself.
Meanwhile, a hostile, gun-toting man named MacDougal shows up, and he seems to have some mysterious plan in mind involving Fiena’s unusual abilities...
What conspiracies await Orphen and company in the homeland of the legendary Deep Dragons?