The end of the world most likely started with a Nintendo 3DS, and a website.

Kosaki Household, 6AM

"…Unn." The black haired boy rolled off his bed and slammed onto the floor. "Gah!" He woke up to the sound of his face slam on the floor and opened his eyes. He looked around the room to see that his entire room was a mess. His desk was cluttered, his closet unorganized, and to top it all off, his entire bookshelf fell onto the house and made a loud bang. "Shijima? What was that?" A woman's voice yelled from downstairs. "Just the bookshelf, mom!" he yelled down to his mother. He quickly got up and lifted the bookshelf up to its original position. He gathered up all his books and put them back into the bookshelf quickly and headed downstairs for breakfast. "Good morning, Shijima!" His mother, Sakuya said to him. She was in her 30s, but still looked young enough to look like she was single. "Morning..." he replied. He sat down at the round wooden table where he and his family ate all their meals. Across from him was his father, Shido who had been reading the newspaper until he arrived. His father gave him a smile and put the newspaper down. "Shijima, I have something I want to give you." His father pulled something out of his bag, which was lying on the ground to his left the whole time and revealed to Shijima a box. "What's in it?" Shijima asked, curious of the contents of the box. His father looked at him with a smile and said to him, "Why don't you find out yourself?" Shijima opened the lid of the box to find a blue and white Nintendo 3DS. "A 3DS?" Shijima asked his father. "Yeah, but this one's special. Go ahead and turn it on." He gestured to Shijima to turn in on, so he pressed the small POWER button, and the system started up. For a few seconds the screens stayed black, and then it started up. On the touch screen was a logo called "Nicaea the dead face network." Shijima stared at the screen in disbelief and asked his father, "What's this Nicaea website?" His father seemed surprised to hear this, and took a look at the screen. "I don't know what this is about, Shijima… This isn't the surprise I was talking about. The surprise was supposed to be a preinstalled version of "Devil Survivor Overclocked." Shijima wondered about this website and took a look into it. The website talked about signing up to see "dead face clips of people you're connected to by fate." He quickly became curious and signed up for the website and took a look on what was on the Nicaea application, which was forcefully downloaded onto the 3DS. On the app were 9 folders. 6 of the 9 folders wouldn't open up and so Shijima checked the last 3. One folder's name was listed as Mail, and another called Team. Shijima wondered what that Team folder was about and opened it up. On the page were 4 slots with his picture in the center on 1 of the slots. Next to his picture was an empty slot on both sides of the picture. He closed the folder, and opened the last folder, which was named Almanac. He opened the folder up to see 13 empty slots. He wondered what they were, but didn't have the time, as he was almost late for school. He closed the 3DS and got dressed into his Soutei High school uniform. The uniform was black with a red tie to finish it off. He packed his 3DS with him and left his house for Soutei High, where his best friend Chitoge Oikawa awaited him.