Available: Ryoma marries another female character
Unlockable Character: Shiro
The boss of this map, Tarba, can be captured by Orochi so if you want get him to your army, you must bring her and protect her until she can land the finishing blow using her Capture command.
Shiro is located in the middle of the map. You must have Ryoma reach him and talk to him in order to recruit him. The desert terrain will restrict your movements but there are several dragon veins in the area that will turn considerable areas to plains. Fliers will not be restricted so you can use that to your advantage and to reach Shiro immediately. Be careful not to carelessly activate these dragon veins or you'll allow the enemies gain the initiative.
Shiro will be aggressive and will actively attack any nearby enemy unit within his range. That's why you need to prioritize getting to him first. After talking to him, regroup with your main army, heal up, and start decimating the scattered forces. Remember to heal in between battles since the enemies here can deal fair damage, scaled on how far you are in the story.