Karlheinz is the main antagonist of the game, anime, and manga of Diabolik Lovers. He is the husband of Cordelia, Beatrix, and Christa. He is also the father of the Sakamaki brothers (Ayato, Kanato, Laito, Shu, Reiji, Subaru, and Kino). Karlheinz is also the King of the Vampires.
Karlheinz is very intelligent and powerful, however, he's incapable of feeling love and affection. This is showed through out flashbacks. He also seems to be a womanizer, as he seduced all three of his wives for his selfish plans. Karlheinz gave them false love in order for them to break their children so that his sons learn love from a human girl (Yui Komori).
He is also the main reason of his children's traumatized childhoods. Karlheinz heavily neglected all of his children through out their lives. However, Karlheinz will punished them if they displease him. This is revealed when Shu had to repeat another year in high school and Karlheinz exiled him to the North Pole, throwing Laito in the dungeon when it was discovered that his son had a sexual relationship with his mother Cordelia, and when Subaru broke a statue of his father, he ended up being sent to the ocean and finding his way home.
He shows up in most of the bad endings in the game and says that he will kill his own sons if they failed him. In fact, Karlheinz shows that he has no problem abandoning his children. This was showed in Lost Eden, as Karlheinz abandoned his illegitimate son Kino as a child to live the Gouls.
It's revealed that Karlheinz admires human emotions, as he himself lacks of. It's the reason why he wanted children so they could have human emotions. In fact, Karlheinz thinks of his wives and his children as experiments and nothing more. Because of this most of his sons hate him.
His plans were revealed that he wanted to create a new demon race, in which he call it the Adam and Eve Project. The plan was that for his sons to find love in a human girl. He wanted the demon race to have powers of demons, but the lifespans of humans.
Due to Karlheinz's intelligence, he carefully planed his progiect. In More Blood, he took in four human orphans and turned them into vampires. However, he only did this so they serve him loyally.
In Dark Fate, it's revealed that Karlheinz imprisoned the First Bloods when the race was infected with a disease that wiped out their kind. When the First Blood Queen's sister went to him to find a cure for her race. However, he instead sent her to the Demon Lord and there she became the Demon Lord's lover. This act revealed that Karlheinz wanted her to birth to a illegitmate daughter and marry that daughter who later be his first wife Cordelia.
His plans were originally that he was going to be Adam and Cordelia as Eve. However, he does show that he will blame others for his mistakes instead realizing his own faults.
Corderlia is Karlheinz's first wife and the mother of his triplets Ayato, Kanato, and Laito. He planned to marry her even before she was born. Cordelia met Kalheinz when she was very young, which he counted her at that age. However, the reason why he wanted to marry her was because of her blood. Because Cordelia had little to no knowledge of love, due her father the Demon Lord neglecting her and her mother died at child birth, Karlheinz took this as his advantage. He gave Cordelia the false meaning of love, teaching her that love was a cruel game, saying it was alright to have many lovers, as well as telling her it was okay to have incest relations (Of which Cordelia ending up sexually abusing their son Laito).
It's later revealed that Karlheinz and his younger brother Richter both fought for Cordelia's heart, which she ended choosing Karlheinz. During their marriage, Cordelia said Karlheinz had often granted her every desire and wish no matter how selfish they were.
When Karlheinz wanted to be become Adam but failed, he blamed Cordelia because she loved him to demon like, without even realizing that he was the one at fault, since Cordelia loved him genuinely and mutual. He then decided that he wanted to have crossed breed children with her. However, Cordelia had a dislike towards children, so he took another step for his plans.
To get what he wanted from Cordelia and to show her that she was replaceable, Karlheinz took in another wife, Beatrix. When Beatrix gave him his two eldest sons before Cordelia the first wife could, Cordelia finally submitted and gave birth to Karlheinz's triplets sons. Unfortunately, the triplets had inherited their father's vampire genes and not their mother's blood.
After this Karlheinz would neglect Cordelia. Once he gave her flowers which had the meaning impossible, their son Ayato would find them and destroyed them before Cordelia saw them, wanting to save his mother from a brokenheart, unfortunately, she saw them and punished Ayato. Karlheinz is also the main reason for who she is, as he transformed her from a meek and naïve girl to cruel and lustful woman.
Despite all of neglect and mentally abuse, Cordeila continued to love her husband very much. Because he taught her the false meaning of love, Cordelia would sleep with other men, including her brother-in-law Richter (which Karlheinz silently encouraged them to), but she never considered them lovers, instead she only called them "the men that desired her". Although, Cordeila had many affairs with many men, her love and body would always belonged to her beloved husband the Vampire King Karlheinz. Cordelia even had a sexual incest relationship with her son Laito. When her husband discovered the unsually relationship between them he didn't punish his wife, but he threw their son into the dungeon as a reminded to Laito that he could never have his mother as a lover.
Unfortunately, Karlheinz would then planned her death. He would let their children do the job, than he would put Cordelia's heart in another body. When Cordelia did died by the hands of the triplets and Richter then came took her heart and placed in a body of a human baby girl named Yui Komori; however, neither Cordelia, Richter, or the triplets were aware that this was planned out by Karlheinz for his selfish plans, which was to create a new demon race that of his own.
When Cordelia came back to life by her cousin Carla the First Blood King, he told her that Karlheinz had the power to bring back the dead and could have brought her back but he didn't. She went to an emotional breakdown and when she to see her husband and to confront him, Karlheinz didn't response to her words leaving her in tears. Before Cordelia died again, she told her son Ayato to make his lover Yui happy. Ayato then went to battle his father for everything that Karlheinz did to their family.
Beatrix is Karlheinz's second wife and the mother of his two older sons Shu and Reiji. He married her after his first wife Cordelia didn't want to have children because she had a dislike towards them.
Christa is Karlheinz' third wife (and later revealed cousin) and the mother of his youngest son Subaru.