That Time I Got Reincarnated as a Slime, Volume 17 (manga)

Now that Rimuru has risen to the level of Demon Lord, the pinnacle of monsterkind, the powers of the world inevitably take notice. Foremost among them are the other Demon Lords, who call a meeting known as a Walpurgis, a space for these fearsome figures to hash out their differences. Though Rimuru secures an invitation to the event, he must tread carefully until he can distinguish friend from foe…