The Isolator, Vol. 2 (light novel): The Igniter — Reki Kawahara

An alien parasite living inside of Minoru Utsugi gives him the power of Isolation--an unbreakable shield that surrounds his body. With this power, he's managed to defeat an evil Ruby Eye. Having done so, he's invited by the Accelerator--a girl named Yumiko--to join a mysterious organization whose goal is to defend humanity from the threat of the Ruby Eyes. Minoru agrees to join, with one condition: Once he has fulfilled his duty, the syndicate will erase all memory of his existence from the world--for Minoru seeks a world without any knowledge of him, a world of total and perfect isolation.