BEAST Ryūnosuke Akutagawa/Synopsis

Plot
A group of children is attacked with one of them being held hostage with their life when Akutagawa quickly cuts his hand off using Rashomon. Carrying the injured male, they head back to their "home", which is a small run-down room with a fire in the middle.

As they chat for a while, one of them reveals a diamond. Explaining he'd witnessed some people in an armed organization talking about their illegal dealings, and after their conversation, one of the males had dropped it. Akutagawa uses Rashomon in an attempt of breaking the diamond, when it doesn't crack from Rashomon's blade, Akutagawa confirms it's real. One of them suggests the group go back to the same area in hopes of finding more diamonds.

As the group begins to head out, the very same armed organization one of them had overheard breaks in and begins shooting everyone dead. Akutagawa, with Gin runs to safety, Akutagawa notices Gin's right arm was injured from the attack. Gin assures Akutagawa that she's fine, Akutagawa asks about the others and Gin gives him a saddened expression. Akutagawa freezes in shock for a moment before heading back to avenge his friend's deaths, running straight towards the group of 6 who'd attacked them. Digging his fingers into a cut on his ribcage from the attack, he rubs his blood onto his face to appear injured. Akutagawa poses as a victim of gun violence to the group. Explaining he witnessed 2 males rob a government currency transport truck after killing the driver and ran away after they tried to kill him.

The 6 males make a plan of robbing the truck before their meeting with the Port Mafia, asking Akutagawa where he saw the theft occur when one of them recognizes him. Akutagawa proceeds to kill them all with Rashomon brutally. Akutagawa, now injured, lays on the grass. Covered in his own and the 6 other's blood, Akutagawa asks himself aloud why he must die, when a voice answers him.

Akutagawa sees a man in black with bandages over his right eye, Akutagawa questions the male if he is with the other 6, and the man in black replies he was going to recruit him into his organization but changed his mind. Explaining he is nothing but an unintelligent dangerous animal, Akutagawa retaliates by attacking him with Rashomon but is easily beaten down. The man leaves Akutagawa unable to move, explaining he will take care of his sister until Akutagawa is strong enough to beat him.

4 years later, Akutagawa lays starving to death by a river. Desperate, he begins eating mugwort he'd spotted when a male comes across him. Using Rashomon to attack him, the male easily dodges. Despite the male telling Akutagawa he was only concerned, Akutagawa attempts to use Rashomon again when the male punches him in the gut and carries him over his shoulder.

Akutagawa is inside a dormitory who answers a call from Oda, the man who saved him at the riverbank, and orders Akutagawa to go to a specific location. As Akutagawa walks up to the location's entrance, a blonde male standing by the door, asking Akutagawa to lend him a hand with a bomber. Despite the yells of the blonde male, Akutagawa walks straight up to the bomber with a hostage. The bomber threatens to detonate the bombs and Akutagawa tells him to do it, acting on his threat, the bomber pushes the button. Akutagawa quickly uses Rashomon to rip the bombs apart, attacking the bomber and pinning him into the wall. Akutagawa prepares to kill him when everyone reveals its an entrance exam, Akutagawa freezes when he figures out the hostage and the fake bomber are siblings.

Later at the cafe, Akutagawa asks if Naomi is really Tanizaki's sister, to which he confirms, Akutagawa replies that little sisters should be treasured. Akutagawa is relieved and makes an order to the waitress before Akutagawa and Tanizaki start a conversation. Akutagawa talks about his upbringing in the slums, his liking of tea, figs, shiruko, and dislikes of soramame, mandarin oranges, and wild dogs. Telling a story of how when he was younger, a wild dog nearly bit off his arm while he was sleeping in the slums as the backstory for his disliking to wild dogs. The waitress then comes by with Akutagawa's order when he slips and Akutagawa quickly uses Rashomon to catch the food and the worker.

Akutagawa tries to attack Oda using his Rashomon, after multiple tries, he is stopped by Oda. Akutagawa calls Oda amazing before calmly sitting back down. Kunikida asks who Akutagawa's mortal enemy is. Oda explains Akutagawa wishes to kill 2 people, that is why he is honing his ability. Akutagawa says one of those 2 people is a male whose face he does not know, to which Akutagawa calls him the man in black, the man who kidnapped his little sister.

Together with other agency members, they approach Ranpo to ask for his help in finding his sister. However, Ranpo refuses and says that it is too much work. Akutagawa firmly replies that Ranpo does not need to investigate and will find his sister on his own. He is then given a card for stamp approval which he needs to get all the stamps of other members before Ranpo helps him. Akutagawa is then approached by Kenji telling him thatt he has work for him.

The next day, Akutagawa and Kenji are at the rice fiels. Kenji teaches him the ways on planting rice. Akutagawa spent days on helping Kenji at the fields. However, on the tenth day, Akutagawa spots a truck dumping waste containers near the rice field and attacks it. Kenji stops him and tells him that killing people is bad and as long as they have the waste containers, the agency can track them. The next day Kunikida informs the two of them who is behind the illegal dumping and reveals that it is a industry-leading pharmaceutical company in the world of mass-produced pharmaceuticals. Kenji then smiles says that it can't be helped but at least the rice paddy is fine and tells Akutagawa that they should continue the rice planting. However, Akutagawa does not respond and rushes out at the agency office.

Akutagawa arrives at the pharmaceutical building and kills the guards in the building. Before going to the head of the building, he is stopped by Tanizaki, Kenji and Oda. Akutagawa and Kenji then go back to the rice fields. Kenji then reassures Akutagawa that they still have time and if the agency manages to prove that it was illegal dumping, they can sue them, unlike natural disasters and tells Akutagawa that he will, for sure, find his sister.

Back at the agency, Kenji gives his stamp to Akutagawa. Kunikida arrives and was asked the status of the illegal dumping case. Kunikida states that the case has been wrapped up and that the men who dump the waste gave the company right away and all that is left to get a warrant. Akutagawa curiously asks the reason why the criminals confessed that easily. Kunikida replies that no one in the city wants to anger Kenji. Kunikida then follows his statement by asking Akutagawa is he is ready for Kunikida's favor and tells him that he will appoint him to the disciplinary committee.