How NOT to Summon a Demon Lord (Manga) Vol. 12 (Kobo eBook)
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 Horn, the lowly adventurer, 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!