Introduces porcupine-derived quill growth genes into the skin of the upper back, shoulders, and outer forearms. The quills lie flat against the skin when relaxed and erect into sharp, barbed spines when the user is threatened or consciously activates them. Erected quills stand 4–8 cm tall and are sharp enough to penetrate clothing and skin. The barbs are designed to break off in an attacker's flesh (like porcupine quills), causing persistent pain and requiring medical extraction. The quill bed continuously regrows broken quills over 1–2 weeks. The modification is purely passive-defensive — it makes the user painful to grab, grapple, or tackle from behind. Gravemoss Biofoundry designed it for people who face physical violence regularly and can't afford weapon-equivalent modifications. It's cheaper than venom glands, less regulated than electric organs, and always ready.