Strait Jacket

Strait Jacket (ストレイト・ジャケット Sutoreito Jaketto?) is a light novel series by Ichirō Sakaki with illustrations by Yō Fujishiro, published by Fujimi Shobo under their Fujimi Fantasia Bunko imprint. It was published in 11 volumes between 2000 and 2010. The series was adapted into a 3-episode OVA series in 2007. A film version of the OVA aired in the United States on the Sci-fi channel.

Plot
It is the world where magic and science coexist. Rayotte Steinberg, a lone wolf "tactical sorcerist", fights against monsters. They used to be human beings, but they had overused forbidden power, "magic", to turn into monsters. What he wears is "mold", the straight jacket that keeps him being a human. What he holds on his hand is "staff", a magical wand that explodes everything. If he casts magic, he moves one step to be a monster. If he doesn't, he will be killed. Among the harsh battles, he will face a sin he had committed in the past.