Many "free injector" APKs found online are bundled with malware or spyware that can steal personal data from your phone.

Automatically snapping the crosshair to an enemy's head for instant kills.

Increases your character's movement speed beyond normal limits. The Risks of Using an Injector

Plot-wise, the story could start with a peace broken. Alex is now a peacekeeper, but an incident occurs where injectors are being misused. The antagonist could be someone who wants to weaponize the injectors on a larger scale. Maybe a new corporation or a rogue scientist.