That Time I Got Reincarnated as a Slime: Trinity in Tempest (manga), Volume 6

TIME TO RETALIATE!

Wielding her new equipment, Phos joins the battle against Demon Lord Clayman in a grand alliance between the Tempest Federation and the beast kingdom, Eurazania. Meanwhile, aware of Milim's secret plan to declare war on Carrion, Stella rushes to the Forgotten City of Dragons, and Nemu heads for the harpy kingdom of Fulbrosia, where they work diligently to prepare. Soon the Trinity will reunite in Eurazania—on the battlefield. Don't miss the climactic struggle between nations, retold from the new, ground-level perspective of three valiant warriors!