Akatsuki no Goei Trinity Complete Edition by Syangrila

The story begins in the near future. The police have lost control over the level of organized crime, in connection with something here and there a lot of crimes are committed. To deal with this problem, the government established a bodyguard academy. Kaito, the protagonist, enters her, and overcoming hard training becomes a bodyguard. On the last day of class, the other students look happy, but not him.
“I'm hiring you as my bodyguard, good luck,” she says haughtily. "What...?" Her determination really makes him seriously think that ... He just wants to protect her ...