The Master of Ragnarok & Blesser of Einherjar: Volume 12 by Seiichi Takayama

Following the decree of an imperial subjugation order against the Steel Clan, five major clans have joined together in an unprecedented military alliance. Fagrahvél, patriarch of the Sword Clan, commands the army invading from the east, and his forces total a staggering thirty thousand! With sheer numbers that outstrip even those of the Steel Clan, as well as a number of powerful einherjar fighting in his ranks, Fagrahvél attacks the eastern border fortress at Dauwe.
Meanwhile, Yuuto is still in the middle of returning from Lightning Clan territory in the southwest...

Faced with an invasion on a scale the likes of which he’s never faced before, can Yuuto come up with a strategy that will break through this crisis?! The popular isekai fantasy novel series continues in this battle-packed 12th volume!