Blood Rain

High and Low: Sword/Masaki comes online at a young age - far too young, as a result of his mother's death. At the time, he doesn't realize what happened, not really. When their parents, his dad and Hiroto's mother, die, Hiroto comes online. As a Guide. After a few years, Aniki comes online too. As a Guide. Masaki and Hiroto don't know what caused it until much later.