"Tell me what a Sabbath is!" Rin yelled, yanking away from Yukio. "A Sabbath is a rare occurrence. It happens when the veil or barrier separating Gehenna and assiah weakens. It's basically a party for demons that takes place in gehenna." Yukio explained.
"A...party? Wait! If the barrier separating Gehenna and assiah weakens, doesn't that mean Satan can escape?!" Rin yelled out.

"Quiet down! As far as I know, He still can't escape. The barrier is strong enough to hold out. Anyway, the Sabbath starts at sunset and lasts until dawn of the next morning. The majority of the stronger demons return to Gehenna to celebrate. As to what they're celebrating, we don't know."
"So...the demons are all going back to gehenna? Then why haven't the exorcists sealed them all in gehenna during this Sabbath?" Rin questioned.

Yukio sighed heavily, "Because if they did that, the demons could combine their strength and come here with Satan. Besides, weaker demons flee from gehenna. They don't have to possess people, and from what Mephisto's said about gehenna, they aren't treated very well.

"Eh? What's all that have to do with us?"

"Not all demons are going to the Sabbath. Some might come for us, after all Satan is our biological father. If we were taken to the Sabbath, Satan could use you to escape. That's why Mephisto told us to stay indoors and protect ourselves. I have somewhere to be during that time, which involves other exorcists so you don't have to worry about me. I'm more concerned about you. Don't leave the dorm under any circumstances, understand?!"

"Okay, okay! I won't," Rin said. "Promise?"
"Promise," Rin answered.