Send them a link to the OST if they're into music. But if you wanna "explain" the game to them, try saying, "It's a PS4 title. Your guy leads a double life while he lives in Tokyo for a year: half the time, you're an ordinary student, but in the other half, you're using the powers of gods, demons, and discount Stands to kick the enemy's ass while utilizing an elemental weakness system that's like Pokémon- and looking cool as shit while doing it."
but that only really explains the battle system, and totally misses the story, which I feel is equally important