Majo no Geboku to Maou no Tsuno

Majo no Geboku to Maou no Tsuno manga summary: The witch Vivian is dying, and she asks her apprentice Betty to prepare the only medicine who can save her. But to get a hand on the ingredientes it's not going to be a piece of cake... because one of them is the horn of the demon king Kinguburu, and defeating him can be a matter of life and death.