That... indeed sounds kind of like Devil Survivor but it somehow seems totally different.
I understood that you already looked up this information but let me tell the differences between our ideas and what I want the RP to contain:
Devil Survivor is about attacks from demons that infiltrated the human realm, the humans have to survive judgement day in order to keep their world and for their race to keep existing. There are seven days in total that they have to survive, the seventh being judgement day. Every day a Septentrion will try to attack the defense towers in the three main cities. Every day these Septentrion get stronger and at some point, only summoners with really powerful demons (like Byakko, Cerberus and Kikiruhime) can defeat the Septentrion.
This all started with an app available for the android mobiles called "Nicaea" which also has a "dead face delivery site". However, humans later find out that these dead face delivery clips are for real. Once they die, they get the choose if they still want to live... if they choose "yes" then they'll become summoners.