In this mission, Marche walks in to the area to discover a clan standing there waiting for you. Somehow they knew Marche would be there. In this battle there are two Thieves, two Bishops, and two Fighters.
You might want to take out the Bishops first, because they both have Cura and might slow things down as they heal wounded units before you can KO them. Another big concern is the thieves. They can steal weapon and steal ability. Having an ability stolen is pretty bad, because it means that, if successful, something that you spent a while learning will go away. Not that you can't learn it again, but that's kind of a hassle. Anyway, steal weapon is maybe even worse than steal ability if you have some rare weapon equipped and it gets stolen. So you should deal with those thieves quickly, whichever way you can. You can make Steal illegal, or disable or immobilize the thieves, or just KO them instantly with a spell or powerful attack. Whatever works. Some of the enemy units have reaction abilities like Strikeback (which means they will hurt you a lot if you use Fight against them, while not being harmed themselves) and Bonecrusher, which is like Counter but with more damage from the enemy.
When all enemies are defeated, you are done with this mission. Marche will wonder how that clan could possibly have known that Marche would be there. He gets a strange feeling of being watched, and is pretty annoyed.