Ragna Crimson 15

To bolster humanity's forces, Ragna personally trains Ruoxi and the remnants of the Argentum Corps in the art of aura control. Deep underground, in a secret layer of Gehenna, Bagram plots the invasion of both human and dragon strongholds across the world. Before long, a swarm of twenty-two million dragons descends on Amen, setting off an all-out war between the Roaring Bloodline and the Solarian Church!

Volume 15 of the Ragna Crimson manga series by Daiki Kobayashi.