Id: Invaded^{[lower-alpha 2]} (stylized as I⊃:INVΛ⊃≡⊃) is a Japanese anime television series produced by NAZ, directed by Ei Aoki and written by Ōtarō Maijō. It aired from January to March 2020. A manga sequel by Yūki Kodama was serialized in Kadokawa Shoten's seinen manga magazine Young Ace from October 2019 to November 2020.

The story follows the investigations of Narihisago, a renowned detective now in prison, who is tasked with diving into the id wells of various serial killers. Two years prior to the current events, Narihisago's daughter Muku was brutally murdered by a serial killer, leading Narihisago's wife to commit suicide. These deaths prompted him to hunt down and murder the killer, earning him his prison sentence. He is still depressed and haunted by his wife and daughter's deaths, but also uses this as motivation to take his work seriously and help stop serial killers; however, as a result of the deaths of his family, he bears a grudge against all serial killers, which occasionally manifests as an uncontrollable urge to kill. Despite this, however, it is shown that the majority of Narihisago's colleagues have great respect for his work. Rookie field analyst Hondomachi becomes an important character during the series after having a brush with death in a serial killer case.

Events take place in a world where investigators have the power to tap into a killer's unconscious and see fragmented parts of their psyche. This is referred to as an "id well", a mental plane that can be digitally entered to collect clues regarding a killer's victims, crime scenes, and motives. As one traverses through an id well, their sights and actions appear as digital projections in the real world for investigators to analyze in real-time. Since a person's unconscious thoughts are rarely organized, everything within an id, including people and locations will appear in a fractured or symbolic state and can only be temporarily put together by someone investigating the id well. Additionally, id wells can only be entered by victims or other killers. While it is possible to get hurt or die in an id well, the Well traveler can simply be removed and re-injected into the Well again, though all previous memories from their time in there will be lost.

Field analysts assist Well investigators using a tool called "Wakumusubi ", a sort of handheld radar gun that detects and collects delicate "cognition particles", given off by a person's intent to kill. The scanner can be programmed to collect the killing intent of a specific criminal and add that information to their id well. This helps flesh out the killer's Well for a more thorough investigation. Additionally, the memories of victims encountered in id wells can also add important information to the environment.

Akihito Narihisago (鳴瓢 秋人, Narihisago Akihito)

Voiced by: Kenjiro Tsuda^[2] (Japanese); Jessie James Grelle^[3] (English)

A renowned detective assisting in investigating and analyzing serial killer id wells. His real name is Akihito Narihisago, but during his time in id wells he is referred to as the brilliant detective Sakaido (酒井戸, Sakaido). In the past he was once a happy family man with a daughter named Muku. Two years prior to the current events Muku was murdered by a serial killer nicknamed the Challenger, followed by Narihisago's wife committing suicide out of grief, leading Narihisago to kill the Challenger out of revenge. He is sentenced to prison for this, and is placed in the maximum security section with other killers. Feeling guilty for not being able to protect Muku, her death continues to haunt Narihisago and gives him nightmares. However, having killed someone, he is now able to enter id wells and retrieve information in serial killer cases. He is shown to have to bear a grudge against all serial killers and on occasion uses the knowledge gleaned from their id wells to cause them to commit suicide in prison, something that creates friction between him and the rest of the investigation team.

Funetaro Momoki (百貴 船太郎, Momoki Funetarō)

Voiced by: Yoshimasa Hosoya^[4] (Japanese); Christopher Wehkamp^[3] (English)

Head inspector of the investigation unit, and a good friend of Narihisago. He worked with Narihisago as a police officer prior to Narihisago's imprisonment. While he has strong trust in Sakaido's detective skills, he worries for Narihisago's mental health. He rescued the last victim in the Challenger case, Kiki Atsukai, but is puzzled by her disappearance and has secretly tried to investigate her vanishing.

Tamotsu Fukuda (富久田 保津, Fukuda Tamotsu)

Voiced by: Ryōta Takeuchi^[5] (Japanese); Justin Cook^[6] (English)

A notorious serial killer also known as the "Perforator" for his gruesome style of murdering victims using a drill. Fukuda has arithmomania, and drilled a hole in his head to try to block out his thoughts prior to becoming a serial killer. He is also scarred on the right side of his face. It is stated that parts of his brain were impacted by the drill procedure, affecting some of his cognitive functions. He is shown to be a very calculating psychopath with a high IQ, and enjoys taunting Narihisago. He is also briefly considered as Sakaido's substitute for id well investigations, whereupon he is named Anaido (穴井戸, Anaido). While ultimately not chosen as a replacement, Anaido and Sakaido do work together as Well detectives in the eighth episode of the series. Unlike other serial killers, Fukuda is the only killer who did not murder Kiki Asukai prior to becoming a serial killer.

Koharu Hondomachi (本堂町 小春, Hondomachi Koharu)

Voiced by: M.A.O^[4] (Japanese); Monica Rial^[3] (English)

A 23-year-old rookie field analyst working under Matsuoka at the beginning of the series. She almost becomes a victim of the Perforator after he kidnaps her, but uses this to her team's advantage. She purposely attempts to commit suicide via the Perforator's drill, generating an id well that ultimately leads to his capture. Hondomachi recovers from the incident, but is left with a hole in her head. Upon killing someone in self-defense during the Gravedigger case, she is recommended by Matsuoka to become an id well investigator. During her time in id wells, she is known as Detective Miyo Hijiriido (聖井戸 御代, Hijiriido Miyo). Hondomachi and Fukuda's relationship becomes one of mutual respect over the course of the series, despite Fukuda's former attempt to kill her.

Kaeru (カエル, Kaeru)

Voiced by: Yume Miyamoto^[7] (Japanese); Sarah Wiedenheft^[6] (English)

A mysterious dead girl whose body appears at the start of every id well investigation. The method of her murder varies depending on the id well of the serial killer being investigated, but it helps Sakaido discover clues about the real killer's murder methods or motives. Oftentimes Kaeru's body is a placeholder for a serial killer's victims in the event that the killer does not remember details of what their victim looks like. Later in the series, Kaeru is revealed to be Kiki Asukai (飛鳥井 木記, Asukai Kiki), the last victim from the Challenger case, who disappeared after she was rescued. Asukai is a telepath who can inadvertently project her thoughts, memories and dreams into the minds of other people and occasionally be premonitory with her dreams. Because of her power, she had intense dreams of being brutally murdered every night by different serial killers, starting with John Walker, who invited other serial killers into her dreams. As her power began to grow out of control and draw people around her into comas, she was kidnapped by John Walker to empower the Mizuhanome system. Kiki's id well is accessible from the id wells of those who used to interact with her, in form of a cockpit chair.

John Walker (ジョン・ウォーカー, Jon Uōkā)

The main antagonist. A mysterious, distorted man who has appeared in the id wells of multiple serial killers, but never speaks. He wears a red frock coat, a gold top hat, brown boots, and a black bow tie. Togo deduces he somehow fuels the serial killer's desire to kill, and Chief Hayaseura deduces he may be a serial killer creator encouraging others to murder. His appearances in unconsciouses have fueled at least five people to become serial killers, leading to at least 44 murders. In the Well world, he appears as the arrogant detective Uraido (裏井戸, Uraido), but is also able to enter id wells without this persona, aware of his own identity. He is depicted as having a God complex and feels no regret for creating serial killers, brushing it off as a minor issue in his overarching plan.

• Blood Lad, another manga series by the same illustrator as the manga sequel
• Hamatora, another manga series with the art by the same illustrator as the manga sequel
• Psycho-Pass, another anime series with a similar premise