Nejimaki Seirei Senki: Tenkyou no Alderamin 6p4w3l

Synopsis 5b451o

The Imperial army is continuing its retreat from the numerically superior Aldera forces at the base of the Alafatra mountain range. They've set fire to the forest to buy themselves more time, but after a few days the fire is beginning to burn out. To buy the time they need to finish the retreat, Ikta is forced to mountain a proactive mobile defense and keep the flames burning. But the enemy general is breaking all the rules, and Ikta can't figure out his game. By the time Ikta realizes what's happened, it's too late, and the enemy battering down his walls with a new weapon and sending their cavalry straight through the flames!

(Source: Crunchyroll)