What a useless episode. It was nothing but talk and flashbacks, no action whatsoever, of any kind. Even the talk was partially stuff we already knew. I guess the event will be crucial for Rimuru, to rise to the status of a demon lord, but at the end of the day, it's not going to be any grand battle, is it? The human invaders could only do what they did with the advance party because of the anti-monster and anti-magic fields. Hinata's whole strategy was also based on that same thing, which is why she dominated the fight.