The Guardian Demon

"When an Angel is banished from Heaven, it has no choice but to become a Demon..."

When Sola Vigil is banished from Heaven, he swore that he'd not break the pact that he made as a Guardian Angel:

Protect the human you are assigned to. At all costs.

And, as the growing fire of war is fanned, Sola is determined to keep his promise. Even if it means being caught in the cross-fire.