Claim: Valkyrie Drive revolves around boys who have been infected with a mysterious virus that allows them to transform into weapons.
Evidence: Each of the series revolves around girls who have been infected with a mysterious virus known as the A Virus (Armed Virus). 
These girls are divided into two classes; Extars (エクスター, Ekusutā), who can transform into weapons when sexually aroused, and Liberators (リブレイター, Ribureitā), who have the power to wield an Extar's weapon form, known as Liberator Arms, through a process known as Drive.