"... Right. It's easiest to summon a Persona in the Dark Hour, which happens after midnight strikes but before time really moves forward to after midnight. The sky and moon go green, water turns into blood, and people who don't have a Persona or the potential to summon one are sealed in coffins. Shadows - monsters called Shadows, not like actual shadows - roam the streets. If they find someone they'll either eat them outright or eat part of their mind and send them into a depression so bad that they'll just sit down and not eat or sleep or drink."

That's... an extremely condensed version of it, but he's had to get used to explaining it fast and simple. ... As simple as possible.