Dieter (ディーター Dītā) is the only remaining child under the care of Mr. Hartmann. Hartmann was trying to continue the Kinderheim 511 experiments on him, until Dieter was found by Dr. Tenma and was rescued. Thereafter, Dieter would accompany Dr. Tenma as a faithful and steadfast companion in his journeys and regard him as his best friend, despite Tenma's desire for him to be given a stable life. Later, as their travels progressed, Dieter would encounter and assist a wide variety of other people, such as Nina Fortner, whom he also befriended and stayed with.
Life under the care of Mr. Hartmann
Dieter lived with Hartmann, a former director of the East German orphanage "Kinderheim 511", who was trying to transform him through abuse so that he would resemble Johan. As a consequence of that, Dieter developed an insecure personality which is shown in his first encounter with Tenma. Shortly after this encounter, Tenma discovered bruises all over Dieter's body and concluded that he was a victim of abuse from Hartmann. Tenma takes him to a hospital and leaves him on guard to nurses for a few hours. Unfortunately, Hartmann comes to Dieter's room by presenting him as Tenma and takes Dieter with him. After Tenma's visit to the orphanage Nina enrolled, he returns to the hospital to pick up Dieter but finds out that Hartmann had already done so.
Tenma finds them and sees this scene: Dieter in a tall royal-like chair and Hartmann, standing behind him, presumably as a manifestation of Johan overseeing the chaos, the event from 1985. Tenma successfully convinces Dieter to leave Hartmann for good, which greatly distresses his foster father.
The following day, Tenma gave Dieter a registration form to give to Erna Tietze, so that Dieter could enter orphanage 47. Dieter refused to leave Tenma and started his journey alongside him, serving as his companion.
In Frankfurt, Tenma parts ways with Dieter and leaves him with Otto Heckel. The two wander around the city for some time but don't get along well, so they also part ways. Along the way Dieter meets a prostitute who is revealed to be a friend of Ayse (a turkish woman who ended up being imprisoned by extremists). Dieter then learns that Tenma had been captured along Ayse. He starts his search for Tenma and goes to a local bar (The same bar Nina had previously been to) and asks if Tenma was seen there. Dieter leaves the place and turns to a basement where he is caught, bound, and gagged by one of Nazis.
They bring him to the place where Tenma is kept imprisoned. The Baby orders one of his men to cut Dieter's throat with knife but the hitmen is gunned down by another. Eventually, the excuse for this is that Tenma doesn't deserve such a treatment as he is General Wolf's special guest.
Wolf's men take Dieter and Tenma and head with them to Wolf's residence. Dieter demands to let him out of the car so he could get back to Frankfurt in time and warn the Turks about the Neo-Nazi's plan of burning down their quarter. The two hitmen refuse, however, and respond by saying that Tenma should see Wolf as soon as possible. Tenma takes his gun and threatens the driver to stop the car. Dieter leaves the car and heads to Frankfurt. Tenma let the driver off and stays with them.
Back in Frankfurt, Dieter meets Heckel in Brücken park and tells him about the plan. Heckel sees this as a chance to steal a precious rug in the process. Naturally, Dieter is irritated by his opportunistic immorality. Their noisy bickering is overheard by a group of men involved in the plot who coincidentally happened to be there. They are captured by Neo-Nazis sponsored by extremists for trying to leak out the plan around all of the quarter. The two are locked in the ground floor, as a building is going to be swallowed in flames, anyway. Nina arrives at the restaurant where The Baby dines. She forces him to tell her the location of where his "main dish" will appear. The Baby tells her instead a "decoy" building and luckily guess the location where Heckel and Dieter are being kept. The things are getting worse, fortunately Nina arrives in time and rescues them. Now, the trio must find the main base where the chaos would start from. Heckel reveals that he knew this place very well because he grew up there and says that this building was just a decoy. He says that the starting place will be the riverside factory where the breeze will begin soon. Nina and Dieter head there, while Heckel goes for the rug. Dieter and Nina appear there in warehouse and see a gasoline spilled on concrete. Nazi appears and encounters them.
Meanwhile, Tenma learns from Turkes that the other evacuation spot is the mosque by the river. By the way, he stumbles upon Heckel and demands from Heckel to reveal the location of plan starting. They appear near the warehouse and attack from behind one of the Nazi guards. Heckel ties him and Tenma goes to the warehouse. Nina threats Nazi with gun and guy is attacked from behind by Tenma, but lighter falls from his hand and falls right into the gasoline. Dieter grabs rug from Heckel's hands and put it on a path. Cops soon arrive and arrest the Nazi. Tenma, Dieter and Heckel escape with a boot and Nina tells Tenma the message about Johan having "two personalities".
Tenma, Heckel and Dieter soon arrive at the ruins of the Hilden and Engels warehouse in Romberg (it was written in the message, Johan wrote earlier in Wolf's dinning room, that he'll be waiting there). They climb at the top of the building and see Johan's message: "Hilfe! Das Monstrum im mir wird explodieren!" (English: Help! The Monster inside me is about to explode!". Tenma then came to the conclusion of what Nina said earlier about the two personalities, Johan has.
Journey to Freiham
Tenma and Dieter parts ways with Heckel and the two head for Bayern. There, they hitch a ride with an elderly couple from England, Mr and Ms. Jones on the way to Freiham. The thing is, husband used to be a policeman and has his old habit of analyzing strangers whenever, he is with them. Tenma finds this quite inconveniently and wonders if the couple plans to turn him in.
A while later, car is out of gas and luckily, a camion appears and offers a room for two. Couple says that Tenma and Dieter shouldn't go out of their way to help them. Tenma makes a promise that they'll find a nearby gas station and tell them what happened here. Tenma and Dieter have troubles with finding gas station and it's getting late.
Meanwhile, couple talks about Tenma. Husband wonders if he would fulfill the promise, however Leia, his wife believes he would. When they notice a beautiful sunset they are reminded of their son: Robert.
Dieter and Tenma appear with gasoline and together with them go to a restaurant. Mr. Jones reads newspapers and asks Tenma what he thinks of Scottish criminal. Jones unconsciously intimidates Tenma by telling him about his police skills and recognition of people at first glance. But the elder falls right into depression when tells that he isn't able to do that anymore and thinks he didn't make an excellent officer then.
Later, couple and the duo take a ride around the town and Tenma gets panicked when sees that the elder turned to the police station. A police passes by car and sees Tenma but doesn't recognize him. Couple returns from station and head to an unknown place behind Freiham, what keeps Tenma and Dieter confused. Husband apologies for taking their time and tells that he just wants to visit Steinbach castle.
Old lady tells that their son wanted them to see a view from that castle, telling that it is a gorgeous view from the castle. Husband says that the son gazed out upon the scenery and that his son is the murderer. One of the reasons his wife and he came to this country was to visit him.
They all later leave the castle and say goodbye to each other.
Mr. Jones tells Leia that Tenma is the wanted criminal and that he saw his picture at the police station. Leia doesn't believes that but looses hope when Jones tells her that he saw him on the picture of wanted criminals at the police station. However, Jones finally releases all of his suspicions toward Tenma as he seemed to have all this time and clearly says that he believes in Tenma's innocence. This cheers Leia and she says that too. Jones also believe that Robert, their son is a good person and admits that the reason he quit being an officer is because he believes his son didn't murder anyone.
Tenma accepts offer from Heckel to treat more people of underworld marketing. One of the patients is a mob boss, Mr. Heitmeyer who had been shot and currently is hiding out in his country home, hidden in the woods of Füssen. After Tenma treated him, Heckel prepares to make some delicious meat. Dieter is playing around and passes by Helmut, bodyguard of Heitmeyer. However, Helmut doesn't respond to any of Dieter's words nor his request to come for lunch. The group lunchs and Heitmeyer talks about money ruining people, as it happened to him. Topic skips to money laundering as Heitmeyer started telling the story about young man leading a large trading organization that monopolized black markets. Money made from illegal activities would pass through the "bank", organization created, money would become clean and legit.
That manipulation later proved to be highly successful. However when the man left the syndicate, greed has spreaded among the majority of people who remained and they all ended being killed and the organization was destroyed. Organization was based in Düsseldorf but the leader gave orders from different locations as he moved from city to city. Heitmeyer says that the "kid" was only fifteen years old when creating the organization and that he might be a student now somewhere. Tenma concluded that the young man is Johan and learned from Heitmeyer that the man left for Munich after giving the last order. Dieter recommends to call for Helmut to join them in lunch. Heitmeyer sent Dieter there. At the same time, Roberto and Eva enter the zone. Roberto kills Helmut and gives Eva a gun. Heitmeyer's transceiver makes a sound sign that means something has happened to Helmut. Tenma is even more worried
when hears from Heitmeyer that Helmut is probably dead. Tenma heads down to the forest to find Dieter. As Dieter is going, he sees Eva but get feared after seeing a gun in her hands. Properly opposite to Roberto's expectations, Eva tells Dieter to go warn the others at the mansion. When she is shot in the leg, Dieter refuses to continue his way and instead comes back to drag her out from Roberto's view. Dieter put her to rest by a tree until Tenma appears and treats her. Roberto misplaces far away from the forest. He was using an aimlessly woman like Eva more of a backup-entering card for mansion but since she betrayed him, the plan fell apart and he left. Roberto alone, couldn't break into the cottage due to a large number of security systems and armed men. In the end, Tenma, Dieter and Heckel left for Munich. Particularly Tenma to find Johan.
Tenma and Dieter meet with Dr. Reichwein in Munich. By the help of his friend Otto, who works at the restaurant, Reichwein arranges Tenma a room in the attic that will serve as his hideout, while he is in Munich. Tenma learns from Reichwein that Johan periodically works as a secretary for Hans Georg Schuwald, the mayor figure for business in Bayern. As Tenma learns where Johan goes daily with Karl Neuman and Schuwald, he leaves the hideout and goes on his own to pursue Johan. Before he vanished, Tenma sent Dieter to live with Reichwein. Dieter realizes what Tenma attempts to do and begs Reichwein to stop him.
A Child's View
Several kids have died, playing the game on the top of buildings. One of Reichwein's patients is a boy Martin who had survived by hitting the first floor awning and landing into the bushes. Reichwein left the room to talk with the desperate boy's mother and tells Dieter to watch over the boy. Dieter enters the room and acquaints Martin. Martin tells him to hand him, his shoes. Martin attempts to leave the room and Dieter tries to prevent him but fails. Eventually, Dieter leaves the hospital with him. The two start heading toward the city.
Martin tells Dieter that life is boring. Along the way, he shows Dieter characteristics heavily influenced by the ones that Johan possesses. He feels enjoyable whenever he intimidates people to feel the ultimate fear. As he did, when an elder was passing by and got stumbled by Martin's stick. Martin pushed hard his stick onto the elder's temple putting him under the high pressure. Martin gets arrogant about this and claims that he will spare his life and moves his stick. Dieter is terrified by Martin's actions. Martin's horrible characteristics have developed due to his overtime friendship with Johan.
Before they reached their location, brainwashed Martin jaywalked, claiming that the "death" isn't something to be feared of, in a boring world like this. Dieter however refused to copy Martin in doing such a dangerous things. Martin finally lead Dieter to a high building. As expected, Martin walks upstairs, but Dieter gets scared as he knows what Martin knows. Martin urges to come with him and succeeds in it. When they come to the top, Martin, staying on the edge, starts explaining Dieter the rules of the game. Dieter tries to convince Martin to stop playing the game and tells him the lighter sides of life that Tenma taught him. Martin just responds by saying that he is the weakling. Suddenly, wind blows and Martin lose the balance, causing him to fall off the edge. Dieter catches his hand and drags him out. Martin finally admits that he is feared of the game but also sadly admits that he can't be like Johan. Martin is teared up when tells that the one who taught him this game is Johan and that Johan will be shot by the asian man. Martin and Dieter return to the hospital afterwards.
Book Donation Ceremony
Reichwein sees the newspapers about Schuwald helding the book donation ceremony at the library of Friedrich Emmanuel in the University of Munich. Reichwein says Dieter to stay at home but Dieter ignores his request and goes with him there.
Nina accidentally meets them in front of the university. A smoke is seen coming out from closed windows. All of the doors are locked. Dieter calls fire department. Nina crashes the window with extinguisher and enters the chaos by herself. She fails to shoot Johan and ends up, injured in hospital. When she comes back from the hospital, Dieter offers her some Kaiser Semmels and spends some time with her talking about Tenma.
Nina is taken under the therapy with Dr. Gillen and Dr. Reichwein to find out more about her memories. She remembers the Three Frogs and decides to go to Prague. Dieter wants to see Tenma and decides to leave with her.
The Doors to Nightmares
Nina feels that something is odd when hears that residents call her by name "Anna". Dieter is confused. The two accidentally arrive in front of the Three Frogs and Nina slowly starts to recall some of her memories and is sure that she knows the Three Frogs building and the mayority of the Michalská area from before.
Nina and Dieter enter the Three Frogs building. Nina recalls the stairs and her "brother" who was taken away. Upstairs, she enters the empty room and feels scared. Dieter doesn't understand her trembling as he sees there's not a single subject in the room. Dieter tries to convince her to give up from trying to reach the memories. Nina remembers Johan's description of the Red Rose Mansion and its location. She continues laundering with Dieter behind, still confused about her. They finally find the mansion.
After some time, they stumble upon the doors that are sticked in the middle of wall. Nina recalls the room full of dead bodies and faints. The room is empty and Dieter is shocked when sees Nina unconscious. Dieter gets panicked, eventually an unknown man appears and along with Dieter took her to the hospital.
Three months passed, Nina and Dieter were living with Jaromír Lipský. He is the one who met Dieter in mansion and with him, took Nina to the hospital. Dieter seems to forgot all the worries with Nina.
Dieter considers Dr. Tenma to be his best friend because he rescued him from an abusive home.
- "Tomorrow will be a great day".
- "Tenma is going to become a murderer!"
- "I have lots of horrible memories, but I don't have to remember those."