"Gakuen Onmitsu Torimono" ("Underground Kids") 1 volume- complete by Nana Shiiba
Kimi hires the services of the school's secret organization because she think someone is after her. This is an earlier short of Nana Shiiba of "Animal Jungle". Same cute art but I like story of the "Fake" extra better. I wonder if the last part has "I'll protect you" theme.