Civil Security arc

The Civil Security arc is the first story arc of the Black Bullet series.

Ten years after the Gastrea parasites begin to claw their way onto the top of the food chain, humanity's hope lies at the hands of Civil Security, an organization specialized in fighting Gastrea. Promoter Rentarō Satomi and his Initiator Enju Aihara are tasked by Kisara Tendō to investigate an area in Tokyo said to be breached by a Gastrea.

Enter: Civil Security
In the year 2021 mankind faces the alien creatures known as Gastrea, a mysterious virus that took humanity by surprise; entering the human body through body fluids, altering the victim's DNA and body structure sequentially. Ten years later, Gastrea has easily taken mankind's spot at the top of the food chain. Presently, a policeman talks to a young kid claiming to be from Civil Security, his age leading the man to believe that he is lying. Scratching his head, the young boy persists, claiming to be the reinforcement sent by Civil Security; informing the man that if he will not trust him, he shall head back immediately. The man solely notes the young boy's persona, and takes a look at his uniform as he determines he is a student. He then asks the young boy, named Rentarō Satomi, to show him his badge as several kids nowadays are pretending to be of Civil Security. When Rentarō gives him his badge, the man looks at it and claims to of never heard of the title of his company before. The two greet one another properly and rapidly get down to business. Tadashima can only sigh as he walks towards the building where the "accident" took place and reveals to Rentarō that reports show that people kept contacting the police about a strange water leak on the top floor, but instead of water, states Tadashima, it was blood. As he walks towards the building, he thanks Rentarō for finally arriving, as it is thanks to him that they can finally investigate further. As Rentarō thinks to himself about Civil Security and its purpose, being to fight against Gastrea, Tadashima brings him out of his thoughts when he questions his Initiator's whereabouts. Rentarō stutters, and assures him that he believes he won't be needing her help for said mission whilst remembering riding off on his bike and his partner falling off.

When the two arrive to the room where Tadashima's men are standing, they are told that two of them entered the room through the roof and window, which greatly angers Tadashima and causes him to grab one of his men by the neck and yell at him for allowing such actions. Rentarō then watches from the side as the man tells Tadashima that they entered the room so that Civil Security would not get all the glory, which angers Tadashima even further. Rentarō simply comes to the door and tells them to step aside. When they do, he kicks the door and barges in. Looking around, he sees nothing, but hears a voice; turning around and seeing a masked man with two policemen engraved on the wall, dead. Rentarō rushes at the man and attacks, but the masked man is quick to block all of his attacks and prove to be stronger. After a quick exchange of blows, Tadashima's men enter the room seeking revenge for their fallen comrades, but in return are killed by the masked man as he speaks on the phone with Kohina. Visibly upset, Rentarō employs his combat style and slightly hits the masked man. Before they can continue, the masked man closes his phone and asks for Rentarō's name, leaving through the window shortly thereafter as he informs Rentarō that no one can stop him. Rentarō is left speechless and out of breath.

Not long after, Tadashima enters the room and calms Rentarō down, reminding him that they must search for the Gastrea. They look around, but find nothing. He sees a family picture and asks Tadashima if the man that lived here was living alone, Tadashima responding affirmatively, said man's name being Sumiaki Okajima. He then inspects the area, and notes the blood on the floor leading to the window; speculating that the man most likely jumped out the window looking for help. The two then leave the building, as well as Tadashima's men, and begin looking for the Gastrea. Quickly enough, they find a trail of blood on the ground, noticing a Spider Type Gastrea in front of them. Before Rentarō can enter combat mode, Tadashima fires a bullet and hits the Gastrea, causing zero damage, but making their presence obvious. The Spider Type Gastrea turns around and begins to attack, urging Rentarō to grab his gun and shoot it with his XD. The Gastrea seemingly falls defeated, but responds when Rentarō is at a close distance to attack. However, before it can attack, a young girl enters the area and claims that she will not allow a Gastrea to kill people, sending it flying with a kick to the face whilst Rentarō watches. Tadashima can only stare in shock as the young girl, pointing to herself, informs him that she is Enju Aihara, Rentarō's Initiator.

Shocking Revelation
Ten minutes before Rentarō and Tadashima encounter the Spider Type Gastrea, Enju, angry that Rentarō left her behind, is confronted by a man covered in blood, asking her for help. Enju, however, asks him if he has any last words before dying. Understanding the situation, Sumiaki solely tells her to inform his family that he loves them, just before he turns into a Gastrea and attacks Enju; overpowering her slightly. Before Sumiaki can attack Enju once again, a bullet hits him, turning around to see Tadashima and Rentarō attacking. Enju, seeing this, frees herself from Sumiaki's previous attack and defeats the Gastrea in mere seconds.

Rentarō puts his head down and apologizes to Tadashima for his carelessness with a low level enemy. However, Tadashima informs him that it is okay and asks him about his Black Bullets that were able to harm the Gastrea. Rentarō tells him that his bullets are created from the very same object that Gastrea are not able to recover from; Varanium. Understanding said reason, he moves on to question Enju's eyes, which turned red when she attacks, only to be told by Rentarō that she is an Initiator, and thus the red eyes. Enju turns her attention to Rentarō, unexpectedly kissing him for acting so brave even when she was not around. Rentarō moves back, leading Enju to kick him between his legs for leaving her behind. Minutes later, Tadashima notes the wound behind Enju's back, seeing her heal it herself seconds later. Sequentially, Tadashima is told by Rentarō that he will show Enju the correct path. As they get ready to go their separate ways, Enju reminds Rentarō of the special sale going on and tells him that Sumiaki asked for his final message to be delivered to his family. Rentarō and Enju leave, leaving Tadashima to speak with one of his men. They talk about Civil Security and its purpose, as well as the Monoliths, pondering what the future holds for them.

Back at the Tendō Civil Security Corporation, Rentarō is confronted by an angry Kisara, his boss, for not receiving the reward money. After chasing him around, she sits and throws one of the two bean sprouts bags Rentarō bought at his face as her stomach growls. The two then talk about how to manage a company, coming up with absurd ideas to call attention to their company. Moving on, Kisara changes to a more sensitive topic and begins to speak about the Gastrea that entered the Tokyo area, claiming that no Civil Security has reported anything related to a Spider Gastrea being eliminated, leaving Rentarō wide-eyed.