Fire Emblem: Path of Radiance/Chapter 7: Shades of Evil

After safely crossing the border, Ike's group decides to search for the diversionary team. Titania thinks she saw someone in the nearby castle and the group goes to investigate. Once there, they are discovered by Daein troops and are forced to fight.

Walkthrough
When preparing, reposition Oscar to the western-most point of the formation and Boyd to the northern-most. Make sure both Oscar and Boyd have a ranged weapon of some sort (if possible) and then save the game. Now, begin the mission.

Send Boyd north and deal with the Daein troops near the treasure chest, they both have ranged weapons so make sure your hand-axe is equipped. Next, use Oscar to defeat the nearby soldier to the west, use a Javelin or Short Spear to avoid damage. However, pay attention to the accuracy percentage, if it's below 65% risk taking the counterattack and use an iron or steel lance.

Once Boyd is finished with the two enemies near the chest, open it to get an armourslayer. Move Rhys, Ike, Titania and Soren west and prepare to deal with reinforcements coming in from the entrance to the castle and Use Oscar to deal with the nearby thief.

Eventually, enemy reinforcements show up and you gain Shinon and Gatrie. Kill the soldier guarding the northern entrance to the room with the treasure chests in it with Gatrie and then kill the southern guard with Shinon. Move the rest of the group into that room and wipe out the remaining aggressive troops. Once this is done, make Shinon and Gatrie trade with any character with fee space and give that character as many weapons and items as possible. Don't kill the remaining soldiers until Shinon and Gatrie have no weapons or items in their inventory.

Once they don't, don't be afraid to kill of the remaining Daein troops. Make sure the one who kills the boss has an open section in their item section. Once all the enemies are dead you have successful completed the mission.