Under The Deep[Re-Writing]

Disaster has now made the world a different place. The government has collapsed and all form of government has been obliterated after the catastrophic event and it is now war. Against the sane, who must try to survive, and the bloodthirsty.
They are called the "Raiders." or Blood Riders as they call them in the West. it is unknown why those people started to want to cause death and bloodshed as Raiders do. Half of the worlds population has decreased and a great portion of who was left are now Raiders.

It's been three years after the catastrophe, and the Raiders have suddenly been killing and kidnapping people randomly. Kids turned into slaves and anyone above 16 is put into prison, turning the compliant into warriors or brutally torturing the defiant. Now, more then ever clothes, food and water is becoming more scarce. Most children have lost their families and friends.
Riyige and Yasu, two siblings who are orphans, have a bad and twisted past with the Raiders. While older brother, Riyige, wants to take revenge and revolt, his sister Yasu just wants to hide and try to survive with their group friends as long as possible.
What is the cause of the Raider's sudden change to kill all? What is Riyige, Yasu and their friends connection with the Raiders? Will the wishes of these two siblings clash and result to kill them and all their friends?