How NOT to Summon a Demon Lord, Vol. 12

In order to cure the Marked Death Disease, Diablo must raid his own dungeon to retrieve a healing talisman from his treasure trove. But when lowly adventurer Horn is carried off by a raging underground river, Diablo must leap in after to save him! Meanwhile, Rem, Shera, and Lumachina continue on as planned, only to encounter a Black Dragon!