Chapter 4: In Occupation's Shadow

Objective	Boss	Units allowed	Units gained
Protect Natalie(the NPC in green) for seven turns	Carjiga	5	Dorcas(speak with Lyn)
Items droped by emeny	Items that can be stole from enemy		Chest/Village
Iron Axe	None		None
Initial Enemy		Reinforcements
8 Brigand, 2 Mercenary, 2 Archer		5 Brigand, 5 Mercenary

Shops:

None

Just do as the tutorial says and stay inside the building for seven turns. It's best to let Kent and Sain guard the main entrance with iron sword, and let Wil go to the left side where the cracked wall is and attack the enemy who is trying to break the wall. Let Florina help Lyn guard the east entrance since she only takes one damage from the mercenaries.
Note: Even if you kill the boss, you still have to survive 7 turns to finish this chapter, and enemy reinforcements will still come.
Note#2: You can let Dorcas talk to Natalie if you want :)

Boss Strategy:
You don't have to defeat him to win, but if you want the exp, then wait until you have finished off most of the enemy units, and let Sain or Kent attack him first, making him weak enough for anyone else to kill.

Reinforcements:
1 Brigand(lower left corner), 1 Mercenary(upper right corner) after enemy's 2nd turn
1 Brigand(lower left corner), 1 Mercenary(upper right corner) after enemy's 3rd turn
1 Brigand(lower left corner), 1 Mercenary(upper right corner) after enemy's 4th turn
1 Brigand(lower left corner), 1 Mercenary(upper right corner) after enemy's 5th turn
1 Brigand(lower left corner), 1 Mercenary(upper right corner) after enemy's 6th turn