Kujo Rina is a chemistry teacher and the homeroom teacher for the 3rd grade D class at Horai High School. She doesn't have a bond with her students. On the school's graduation day, Kujo Rina is pushed from the 4th floor and falls down. She is able to glimpse a school uniform sleeve on the person that pushed her. At that time, she wonders why she was pushed and that she does not want to die.

There are over 600 orphanages across the nation, housing approximately 30,000 children; Most of them had been abused by their parents. Maki, was placed into the orphanage "Kogamo no Ie", after her mother, Ryoka, was arrested and jailed. There she was handed over to the care of Kana, and also Sasaki, the eccentric caretaker of the home. Under Sasaki's management, the home is a calm and safe haven from all the madness of the real world. At the home, Maki befriends 3 other little girls, who all go by their nicknames instead of their real names. Piami who plays the piano really well, Bombi who came from a very poor family, and Post, who is the leader of all the kids.

The Security Guard Center sets the stage for this drama that stars Mamoru Shinomiya, a newly-hired emergency responder. Together with his brilliant colleagues, all of whom have colorful personalities, they tackle one emergency after another with flying colors and restore the safety and security of their clients and the public.