I don't remember what episode it was in but when milim found out about rimuru. milim watched rimuru through the orb and apparently there were also demon lords there so maybe everyone has known rimuru for a long time. I knew rimuru before milim and rimuru were friends.
There was only Clayman, Frey, Milim and Carrion when Milim saw through a crystal ball that rimuru was a Slime Episode 15 at the end and in the episode 16
Yea it is The one ifrit and Veldora playing shogi and Raphael came all of sudden asking Veldora to acquire ultimate skill Both ifrit and Veldora scared of her I forgot which ep it is