So, the world is going to end. Seven demons will attack several focal points (all conveniently located in Japan), and after the seventh demon is slain (if humanity survives that long), someone will gain an audience with the 'system' behind it all and will be granted the power to re-write the rules of the world. The leader of a shady organisation that has been preparing for these events, who is a total bastard who doesn't think twice about sacrificing people to further his goals of survival, is going to instate a 'meritocracy' where those with power are served by those who have none. Hibiki, a high-school student who has gained the ability to summon powerful demons through an app on his phone, will cooperate with him to save humanity, but won't stand for this utilitarian world being created.
The series is based on an RPG by Atlus, also known for their Persona series of RPGs, two of which have been animated. The plot and monsters summoned are reminiscent of those series: Atlus has a knack of tapping into some weird subconscious fear of the occult and technology, and they've done it again with this one. But all the plot can't disguise that it's actually just a series of fights of humans and their summoned demons against the seven 'bosses'. And in the end, we were getting a bit bored of it, even though it's only 12 episodes long.
All in all, a 7.