Denkou is a genderless child robot with the ability to turn invisible. Denkou primarily appears in the episode Into Thin Air of the 2003 series, and briefly cameos in the episode Journey to Tomorrow. and also appears in Akira Himekawa's manga. They also make an appearance in the 2004 video games.
Denkou was originally made by the Swiss researcher Dr. Emil in his mountain laboratory. However, before being activated, Denkou was soon stolen by the gangster Skunk Kusai, who sought to use Denkou for criminal purposes. Skunk imprinted on Denkou and initially acted as a parental figure, and tricked them into stealing under the impression that it was a game. Skunk had Denkou steal mostly from museums and jewelry stores.
Denkou sneaks into Astro's school while invisible, eager to observe other children and their class activities. They are soon discovered after school, and they quickly befriend Astro and his friends.
Denkou had no concept of good or bad because of their initial upbringing under Skunk, and they even brought Astro stolen polished gems as a gift. Denkou was so naive that they allowed Skunk to attach a bomb-rigged belt onto them as part of the "game". However, Skunk left them for dead after stealing a crown, only saved at the last minute by Astro. Denkou then goes back to Switzerland with Dr. Emil, still friends with Astro and his classmates. Denkou appears briefly in episode 48, watching Astro's speech with Dr. Emil, implying that he is raising Denkou like his child.
Denkou has the appearance and personality of a very young androgynous child, with fluffy bright green hair and a green caped jumpsuit. Denkou is adapted from the Light Ray Robot, who appears in previous Astro Boy series. Denkou's name is originally pronounced in the Japanese version as "den-koh", but in the English dub it is pronounced as "den-koo."
Denkou appears as one of the bosses in the Game Boy Advance game Astro Boy: Omega Factor. They are one of the world's strongest robots who served Shadow, and the player fights them after North. During their battle, they will run around the stage, leaving timed bombs in their path while the player must chase after them. When they turn invisible, the player must destroy one of the re-generators glowing in the area to disable this ability.
Denkou is also in the Playstation 2 game, where their story is changed; they have been stolen by Dr. Tenma and he uses them to steal jewelry. Denkou also appears in the Akira Himekawa series, which follows a story similar to their anime episode.
- Denkou's pronouns change between releases. The English dub and Himekawa manga call Denkou by "she", and the video games and English version of the official Osamu Tezuka website call Denkou "he".
- However, in the original Japanese text and audio, Denkou is never referred to by any pronouns, leaving them androgynous. Denkou does use "boku" when referring to themselves, which is used by young boys and tomboyish girls. It is possible that Denkou picked up "boku" from hearing Astro and his classmates talk.