|“||The terrorist might still be prowling around.||”|
–Kouta's Father, speaking sadly prophetically
Kouta's Parents have a clear impact on the series, even if they are not seen much at all in-series. They lived in Hokkaido, the northernmost island province in Japan, though their life there is never depicted or discussed. Like many secondary characters in Elfen Lied, their given and family names are never given.
Nothing is known, or implied, or spoken of the fate of Kouta's mother, although she was presumably Kanae's mother as well. It is not even known what their relation to Yuka's parents was, but if Kouta and Yuka were first cousins, then two of the four parents would have to have been siblings, or perhaps first cousins themselves. If so, which of the two were related is still unknown. An indication of which parents are siblings comes through Yuka calling Kouta's father "Uncle," but "Uncle" is also often used for older men a person knows, so it's not concrete. In Japanese, Kouta's father's dialogue regarding Yuka and her mother is more familiar than how a brother-in-law would speak to his sister-in-law, suggesting a blood relation with Kouta's father as the older sibling.
Since no mention of the Kakuzawas' plans includes anything about any family except their own and Lucy's, it can be assumed that the fate of Kouta and Kanae's mother was not driven by events before or during the series and its flashbacks. Not even her complete absence is truly acknowledged, and she is not brought up in any way, again, save for the implication that she must have existed.
Whether Kouta's family had its roots in Hokkaido or one of the parents originally came from Kamakura, the children and their father are first seen chronologically while visiting Yuka's family for the summer in Kamakura. This trip also happened to be the summer a young orphan little girl reached the limits of her endurance and murdered four other orphans who had abused and possibly betrayed her.
Any speculation about a possible romantic relationship between Kouta's father and Yuka's mother must be tempered by the thought that they could have been the related siblings in question, though at no time do the two refer to each other by sibling honorifics in the brief (manga-only) scenes they do interact. Yuka refers to Kouta's father as 'Uncle' at least once, but even when speaking to Yuka's mother on the phone, Kouta does not call her Aunt. A possible reason for this is that especially in Japan, 'Auntie' can be taken as an age-related pejorative and insult.
No information exists about what occupation Kouta's father held, nor if the family lived in an apartment or a house in Hokkaido. Likewise, his mother's occupation is unknown, though it is possible that whatever job she had kept her from visiting Kamakura with her husband and children during the summer. Also possible is the idea that Kouta's mother is deceased before the story begins. Kouta's father has a very protective side toward his children which could either be due entirely to his wife's death, strengthened by it, or just parental instinct. This protection extended to him telling Kouta he wasn't allowed to go out and meet his new friend. Told nothing of the girl, the father wished to keep his children off the streets to avoid them possibly running into the murderer responsible for killing people in their homes, who in fact was the friend Kouta wished to see.
What part of the summer Kouta's family arrived in Kamakura during remains unknown, but they were there during its latter part, intending to cap off their trip with the Kamakura summer festival. Gaining his father's permission to go out again, Kouta spent a day with Lucy that cemented her romantic feelings for him, and, not wishing to hurt her feelings, Kouta explained he was attending the summer festival with his cousin. Lucy resolved to surprise him at the festival, where the father had taken Kouta, Yuka, and Kanae. Events took a deadly turn when Lucy arrived and saw that Kouta lied, as he was embracing his female cousin. Though he hadn't meant to hurt her, an embittered Lucy couldn't distinguish between this lie and another she had possibly endured.
When Lucy killed several people around her in a fit of despair and rage, Kanae witnessed it from behind a festival stall. Curiously, Kanae claimed to have seen Lucy's "arms." In the chaos following the murders, Kouta's panicked father found him and Yuka but was alarmed to hear they'd lost track of Kanae. When they found her, both her family and the authorities dismissed her claim about a girl with horns killing everyone, choosing instead to believe a bomb had gone off. In any event, Kouta and Kanae's increasingly worried father made a choice to take his children back to their home in Hokkaido ahead of schedule.
The manga and the anime vary as to who is there to see them off at Gokurakuji Train Station. In the manga, it is Yuka and her mother. In the anime, two versions of the scene appear: in Episode 2, Yuka is there to see them off with an unidentified, yukata-clad man beside her, and in Episode 12, Yuka is alone in seeing them off. In either version, waiting in the background unseen was a vengeful Lucy, who boarded the train without anyone's knowledge.
Perhaps because of the murders and the late hour, the family had an entire train car to themselves. Leaving Kamakura appeared to relax the father, who read the newspaper while his children fought over Kanae's account of the festival murders. A disbelieving Kouta accused his younger sister of lying, unable to comprehend how the girl he knew could have done such things. Lucy came out of hiding as Kanae insisted she was telling the truth, and a rift was further driven between the siblings as Kanae urged her brother to run away before the horned girl killed him too. Kouta slapped her and demanded she apologizes to his friend and also said he hated her for lying to him. As Kanae cried at the thought of Kouta hating her, she was viciously killed by Lucy, split in half at the waist. A shocked Kouta had no time to grieve and regret his words before the tragedy doubled.
The manga and the anime differ on the details of what followed next. In the manga, the sight of his dead daughter enrages their father, who rushes at Lucy. In the anime, he only has time to register that Kanae is dead. In either version, Lucy swiftly decapitates him, and his head lands at Kouta's feet. Lucy left Kouta alive, saying she spared him because they were friends, though it was unclear if she still thought of him as such. She turned to leave, saying she would go after "that stupid girl" next, which spurred Kouta to launch himself at her. To her surprise, he only shook her and pleaded with her to stop killing people. The gravity of what she'd done sunk in and Lucy ran away, escaping through a hole she made in the roof of the train. She left Kouta alone to struggle with the events of what happened, and it was so traumatic for him that he erased all memory of that summer from his mind, inventing new reasons in his mind of how and why his father and sister died.
Yuka attended the funeral for her uncle and cousin and heard whispers about what had become of Kouta. Since the train had not gotten far from Kamakura, it seems possible Yuka's mother was asked to identify the bodies. Kouta does not directly mention verifiably living grandparents or other aunts or uncles, so she would possibly have been the closest relative available unless his mother was still alive. Kouta's exact whereabouts between the murders and his entry into college are unknown, and he is assumed to have spent those years with relatives, though which side of the family had custody of him is also unknown.
The burial place of Kouta's Father and Kanae is left unknown too. Years later, Kouta returned to Kamakura, to encounter both Yuka and Lucy once again, though he remembered neither of them. Lucy's new personality, Nyu, had no memory of him either, nor that she was the killer who ruined his life. Yuka took early note of the fact that Kouta's stories of Kanae dying from a long illness and his father dying in an accident did not meet up with the truth of their deaths, but failed to bring it up out of reluctance to bring up such awful memories again.
As the series came to a conclusion, Kouta's memories were awakened, leaving him furious with one he saw as a friend. Lucy's efforts to explain and apologize were harshly brushed aside, though Kouta showed sympathy toward her, or rather, the girl she used to be, and was willing to tolerate her existence so he wouldn't lose Nyu, whom he had come to view as a vital member of his family. In the manga's conclusion, Kouta is a mature man and a father himself, and he resembles his father at that same age.
While Kouta's mother exists only as an implied character, his father stands out for several reasons. His caring and protective nature were passed on to Kouta, who, along with Yuka, gave a home to young women in need of help. Like his son, he was ultimately unable to protect those he loved from the dark forces around them. Lastly, his murder and that of Kanae seemingly made the love between Lucy and Kouta an impossible one, as Kouta's anger and wish for vengeance toward her for her crimes against him were only barely brushed aside as he realized he would lose Nyu if he turned Lucy away.
- In Yuka's flashback to Kouta and his family's departure in Episode 2, Kouta's father is wearing glasses. Much like Yuka's father, they never appear again after this instance. His clothes are also different in color than they would be shown to be later in the anime.