Something like that.

But -- yeah. They took in children to 'protect' them and some others after the virus. In exchange for their blood. We're at war, trying to even the odds with some weapons and tricks up our sleeves but it isn't a guarantee.

[The Cursed Gear utilizing the power of demons, pills to increase their synchronization with said demons, the Seraph of the End experiments. All of it. In attempt to come out on top, fighting over said experiments.]