Prime Barrier

The Prime Barrier is a part of the physiological makeup of Homo superior that prevents them from deliberately killing a living thing.

In the first episode, an Ultra field agent is goaded in attempting to shoot Jedikiah Price, but drops the gun after experiencing pain from the Prime Barrier.

When a bully attacks Stephen Jameson at school, Stephen retaliates by using telekinetic force to choke the boy, but the Prime Barrier kicks in and briefly renders Stephen unconscious.

Ultra's Anax Project allowed John Young and Killian McCrane to overcome the Prime Barrier, granting them the ability to kill. John being the truly successful outcome of the project, as it made Killian insane.

In "Sorry For Your Loss", Darcy Nichols used a gun to shoot Ultra agents in the leg, demonstrating that Tomorrow People are able to use deadly weapons if their intent is non-lethal.

In "Limbo", a Tomorrow Person named Michael turns out to be a serial rapist. He beats Stephen unconscious, then throws him into a sewer. This shows that the Prime Barrier only extends to the deliberate taking of a life, and does not prevent causing physical or mental harm, nor actions that indirectly result in death.