
Didn’t they say that if two kings have sex one of them dies?.. so last page, shouldn’t the blue king be dead?

Sorry, English translation are up to chapter 6, and as I pointed the sex scene is from "raw" chapter 10 (actually it's in Spanish, not in Japanese, but anyway) and since it's from the raw I added Spoiler at the beginning.
The conversation about two kings killing each other, or at least one of them dying, is in chapter 6, when Hink is talking to the Black king http://www.mangago.zone/read-manga/5_nin_no_ou/uu/m_chapter-6/pg-9/
Although I can’t read them I saw the other chapters and understood somewhat from the pictures