Seraph of the End: Within Dark Waters

After a deadly viral outbreak; a poor group of young children are left to their own devices in order to survive the new world.
After facing off between their own battles, the children must work together to fend off vampires, sickness, the Four Horsemen of John, and thieving kids of all ages.
Though only one question remains unanswered.
Do they have what it truly takes to survive?