ObsidiusMaad

Sora and Shiro are a pair of siblings, brother and sister, who are well known as brilliant. Yet they are NEETs - useless to society, and (Not in Education, Employment, or Training) - and even worse they are completely house-locked shut-ins (hikikomori!

In Mikado City, a "gate" to a different world is opened suddenly one day. Monsters called "Neighbors" start appearing from it, everyone is afraid of them because Earth's weapons don't work against them, but a mysterious group starts fighting off the Neighbors.

It’s been one year since the failure of the Black Rebellion and the supposed death of Zero. Britannia has assigned Area 11 a “correctional education” status, where Elevens are made an example of by brute force, to try to prevent any future uprisings and suppress rebellious thoughts.