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5 becomes 9’s best friend and they share a strong bond with one another. He is also the apprentice of 2, with whom he shares a special bond. He lost his left eye during a machine attack some time ago, but, as he tells 9, losing it makes concentrating on just one thing at a time much easier. His weapon is a crossbow along with knives, needles, grappling hooks and other weapons which he stores in his quiver. The Scientist remarked that 5 was the first of his creations not to run off or explore the workshop; 5 was very trusting of the Scientist. He has two buttons on his front to fasten his skin.