About
"A" is the twin brother of Lan, who was formerly known as C. A is a test subject of military project "Clovers." Along with B and C, he has a rank of a three-leaf. A is easily swayed by emotions and quick to get violent. He is obsessed with his brother C, not wanting for him to get close with anyone else.
A is the one who killed B, because B and C got close to each other. As a result C ran away from the cage out of fear that A might hurt someone else.