Eri Shiina/Plot

Chapter 4
She is officially introduced in Chapter 4 when she is named by Yuri. She was among the rest of the Battlefront members when Otonashi came to make his decision of rejoining.

Chapter 5
Shiina joined alongside the rest of the Top Brass to eat out in celebration of Otonashi's return. However, she mostly remained silent and kept to herself as the chapter progressed.

After they all finished eating, Shiina left under circumstances that she had work to do. While not clearly stated, it may have been an assassination or observation mission ordered by Yuri Nakamura.

Chapter 6
Shiina was amongst the rest of the battlefront when they assembled for their daily meeting. She promptly left after they were dismissed by Yuri.

Chapter 7
In the beginning of chapter 7 stars Shiina's major debut, beginning with the callouts to meet between Shiina, Takamatsu, and Hinata. When Yuri finally declared that Otonashi was finally found, Hinata observed that Shiina had a look of surprise on her face before it quickly returned to her normal poker face. Shiina questioned why they were called and to everyone's surprise, immediately retorted with a firm denial when she knew what Yuri's purpose was: Bring Otonashi back to the battlefront.

Tensions amongst the members present in the room increased when Takamatsu, logically, thought it was too quick of her to reply. She instead gave him a glare but returned her gaze to Yuri, saying she didn't want to participate in the operation. Given that this was unusual behavior from Shiina, Yuri replied with a snap-like connotation.

Wanting to poke Yuri's brain around the idea of bringing Otonashi back, she asks if they really needed Otonashi back and if it was just a hunch on her part. Given that Yuri's hunches usually lead the battlefront to success in some shape or form, there is a good chance that she may have partially agreed with Yuri's viewpoint. However, Yuri denied it being a hunch and instead wanted to recruit him because the success he brought to the battlefront was the biggest success of their entire lives: Moving on. That success can lead them to more success in what the battlefront is running now.

However, Shiina uses Yuri's logic against her in their argument. She says that because Otonashi was able to help everyone move on from the afterlife and move on himself. Adding on their argument, she reveals that their reincarnated lives are basically a repetition, a testament to them not learning anything from the afterlife.

She then asks Yuri to forgive him and to not recruit him back into the battlefront.

Later on, Hinata notes to Otonashi that Yuri made a compromise to the operation, saying that instead of seeking him out to rejoin the battlefront, they will instead make his life as easy as possible. While skeptical, Shiina agreed.

False Backstory
As a young kid, Shiina was working in order to pull her weight around the house. It seemed to her that knives were just an extra step when she can easily do something with her hands, to the point where she developed calluses. One time while playing with a knife, she accidentally cut herself on her hand, effectively going through the callus with ease. That was when she noticed the sharpness of knives and she began learning more about them, even going as far as maintaining them.

Eventually, her interest in knives became more of an obssession to the point where she injured herself severely with intention. When asked by her parents why she would do such a thing, she said that she sharpened the knife and wanted to see how deep it would go. She recovered, but the scar on her arm bothered her so she brought the issue up with her father. He brought her black armguards for both her arms and she gradually became accustomed to it, wearing it for every occasion with the exception of special events.

When the wars continued to brew on the horizon, everyone contributed to the preparation of the village including the children and Shiina. Even though Shiina was still a bit young, her father quickly taught her how to use kodachi as an offensive and defensive weapon. However, she had doubts as to how practical it would be in a fight against an enemy. When the wars drew close to their town, everyone stood at the ready. When the rumbling increased, Shiina succumbed to fear and began to ran away before her mother stopped her. Instead of berating her, Shiina's mother told her to wait inside the house for them. After she hid, the battle commenced and the unknown enemy forces attacked and won but with great losses on both sides. Her parents were killed in the battle.

An order was given by an enemy commander to search the houses. A soldier walked into Shiina's house and discovered her, quickly reacting as if it was an enemy but realized it was only a child. Feeling sympathy, he took off his helmet and sat down in front of her, observing.

Shiina sees this and realizes that he's not there to harm her. She slowly moves the knife over to the person as if to offer it to him, but he only replies to keep it.

Mission
The chapter then skips to one of Shiina's assassination missions.While she took it as more so of an observation mission, targets were confirmed to appear for the objective they were trying to protect. She stood on top of a tall tower inspired by France's Eiffel tower.

Ooyama then mistakenly calls her name out over the radio to point out that there was movement in the building opposite of her. She observes the location where the movement was and through her binoculars, she recognizes a firearm that looked similar to a sniper and tells Ooyama quickly. He shoots the sniper and she complements him on his shooting, but he then notifies her that there was a person climbing the same tower she was on that fit the same description as the person he just shot.

Shiina quickly moves so she's hiding behind the ladder that she climbed up on. The person proceeds to set up their rifle and lays down in order to get eyes on the target that Shiina and Ooyama were protecting. The person's phone rings and it became quickly known that her partner, which is assumed to be the person Ooyama took out, was eliminated. The person knowingly says that she'll handle it and the call ends. Shiina quickly assassinates the person by slitting her neck and grabs her phone. Noting it's importance, Shiina switches radio channels to contact someone that she found something.

Chapter 9
She was present for a Top Brass meeting.

Chapter 10
She assisted with setting up the concert alongside the rest of the Top Brass and The Guild. Assigned to the rooftop, Shiina maintained eyes generally outside of the stadium as Girls Dead Monster performed.

Fateful Meeting
Shiina ran into Otonashi as he just left Yuri's office. After a bit of chatter, she explained why she was inside the base: To train as she couldn't sleep. He asked to join her, though under a pretense that he would receive a tour but she allowed him to come and train with her.

Training and Bonding
During the training session they worked on various exercises with Shiina guiding Otonashi every step of the way. At one point, Shiina injured herself on her tricep, to which Otonashi grabbed a medical kit and applied aid to her. At one point, Otonashi was unable to locate antiseptic which Shiina pointed out to him. Claiming it was unnecessary was when he told her that she was a fool, to which she reacted by making a noise similar to a brief chuckle. He thanked her for the training session and she left him.

The Club
Shiina participated in the operation that consisted of her, Hisako, and Otonashi, which was to assassinate an individual who was one of the main leaders of the Yakuza. After Otonashi and Hisako entered the club and passed two security checkpoints, Shiina arrived beside Otonashi who had him follow her to his appropriate floor before leaving him.

Otonashi noticed the target's arrival and notified everyone, with Shiina making her way to Otonashi's floor. He identified three guards and Shiina took down two. The third and final guard moved over to a place where Shiina couldn't access him for the time being, causing Otonashi to intervene and have him move to a different spot or conduct a takedown himself. By the time Otonashi arrived to the final guard, Shiina was already in the process of killing him, sticking a knife into his heart.

In awe, Shiina directed him to bring the target here while she dealt with the body. Otonashi brought the target and said something to catch her interest, before he turned around and aimed his gun at her. Beside the target was Shiina, who had taken out her kodachi.

A Gift to Shiina
After the events of The Club, Otonashi and Shiina are engaged in some more intense training, with Otonashi being slammed into the ground. She commented upon him improving but let him know that it was the end of today's training for him at that point.

Otonashi, feeling thankful to Shiina for various reasons, wanted to give her a gift and convinced her to go topside with him. She hesitantly cut her training early and went with him topside, to where they entered the mall and walked more inwards. Otonashi instructed Shiina to stay against a wall and as she waited, Otonashi had brought her a toy puppy and placed it in a gift box. Shiina had opened her eyes and opened the gift box, but fearing that it was something that could catch her by surprise, she closed her eyes the moment she opened it. Otonashi, seeing as she's never really off her guard, takes matters into his own hands and takes out the toy puppy, placing it on her hands. She opens her eyes by his instruction and immediately finds out what his gift to her was.

She looked at him after mentioning it was his gift to her, and immediately began hiding her face. Satisfied, Otonashi began to leave the mall before Shiina stopped him in his tracks, tugging on his coat. They then walked side by side to leave the mall, with Shiina holding onto the puppy tightly.

Convincing Her
Following not too long after the events of Otonashi and Shiina's training session, Shiina finds herself in the Battlefront's meeting room, attempting to convince Yuri to allow Otonashi to participate in her solo operations. While not explicitly stated, Yuri and Shiina engaged in a long conversation that battled traditions and practicality, but Shiina remained firm in her position. Tired, Yuri gives up and concedes, making sure to notify Shiina that 'Training Day' is coming up and to pass along the message to Otonashi as well. She agrees and leaves Yuri alone.

Operation Breaking Even
Soon afterwards, the operation for Shiina and Otonashi began. Standing on top of an adjacent rooftop, they looked down at the city below, engaging in idle chatter and double checking their gear. Shiina notices that Otonashi's radio wasn't properly attached and fixes it for him. The time for the operation had hit and Otonashi had grabbed onto Shiina. Equipped with her harness and grappling hook, she fires it to the target building in which the top floors were still under construction. Jumping off the building, they both land successfully but Shiina sustained minor injuries. They proceeded down the building in attempt to find a server room, clearing each floor. Approaching another floor, they hear footsteps echoing through the stairwell. Otonashi attempted to aim, but Shiina put down his gun, indicating that she would handle it.

The guard appeared at the steps and Shiina bashes him against the wall, rendering him incapable of fighting back. They drag him inside the floor they were about to clear. Shiina notices that the outside appearance of the guard was nothing more than a ruse as he was conceal-carrying a pistol within him, in which Otonashi knocks the guy out after receiving information. Shiina comments on his ruthlessness and points out his assertiveness. She then proceeds to follow his order to head to the server room. While in the room, Shiina contacts Otonashi to notify him of more guards on the way up to check on their friend. She finishes her objective and heads up to find Otonashi apologizing to the people he just murdered.

She noted to him that he didn't have to apologize, and the conversation steers to how she views him. He eventually tells her that he doesn't like how her personality is somewhat merging into his. She then says that he's always acted like this, indicating that his ruthlessness had already came from his occupation. He somewhat concedes, rhetorically asking her if she's smart, to which she replies that she'll be whatever he wants her to be.

His Place
Otonashi and Shiina arrive at his house to clean up before he drops her off. She showers, then proceeds to enter Otonashi's room with a towel still draped around her. Feeling extremely sleepy following the operation, she jumps onto Otonashi's bed and knocks out within a couple seconds. He pleads her to dress up and leave, citing different reasons but eventually gives up. He drapes a blanket over her and leaves to go to the bathroom.