KaiShin

KaiShin is the slash ship between Kaito Kuroba and Shinichi Kudo from the Detective Conan fandom.

Canon
Shinichi Kudo and Kaito Kuroba, the current Kaitou Kid, are rivals and occasional allies. Shinichi, as the shrunken Conan Edogawa, and Kaitou Kid primarily interact during heists. Kaitou Kid, whose goal is to find the gem Pandora, challenges jewel owners expecting Conan Edogawa to show up and try to uncover his tricks and unmask him. Conan Edogawa uses his wits and gadgets to protect the gems and attempt to unmask Kaitou Kid. Although Conan sometimes manages to stop Kid from escaping with the gems, Conan has never succeeded in completely outwitting Kid and revealing his true identity.

Conan and Kaitou Kid frequently team up in the face of a common enemy. If Kaitou Kid has been framed for a theft or murder he often disguises and assists Conan during these investigations. In these situations Conan usually lets Kid get away without a challenge in return for the favor.

Kaito and Shinichi met for the first time during the clock tower heist. During this heist, Kaito attempted to steal the hands of the clock, which was supposedly lined with diamonds. Throughout the course of the heist, Kaito struggled against the police force as they tracked his movements, something he usually didn't have to deal with when he misdirected them. It was revealed that Shinichi was directing the police force from a helicopter circling the clock tower. As part of the heist, Kaito covered the face of the clock with a white sheet on which he projected a picture of the clock without hands. Shinichi discovered this and shoots at the screen form the helicopter. Before the two could lay eyes on each other, Kaito escaped into the crowd, but he noted this heist, with Shinichi's presence, was different from his other ones. While Shinichi, even after the that first meeting, didn't catch the name of the thief attempted to steal the hands of the clock yet. Their next meeting would be the first time they meet face to face.

Their next meeting was after Shinichi was poisoned, and became Conan. The Black Star Heist, was their chronological first meeting, being earlier in the show than the Clock Tower Heist. In this episode, Kaito attempted to steal the Black Star, a pearl owned by the Suzuki Family. Conan, currently living with the Mouri Family, was invited to try and stop Kaito from stealing the Jewel, as his guardian, Mouri Kogoro, was a famous "detective". Conan managed to figure out the heist note and knew where Kaito would appear, and went to confronted him, setting off a firework in order to alert the police to his location. Kaito managed to escape though. He left a note stating that this was just a practice run, an April fool’s joke stated at the top of his heist notice, and that he will return to steal the pearl on a ship carrying the Black Star. When the day came for Kaito to attempt to steal the gem again, He managed to get the upper hand to Conan, by disguising as his childhood friend, Mouri Ran, and when Conan figured out, stating that he left her tied up naked in a boat to bluff and distract him, Kaito once again fled away successfully.

Fanon
Ever since the introduction of Kaitou Kid in Detective Conan, he would occasionally featured in the story and the movies. Many fans noticed their behaviors to each others, Kaito seems to be anticipated whenever Conan attends his heists. Conan make the heists more challenging for Kaito, while Conan views the heists as entertainment. Also, Conan appears to be able to 'sense' Kid's presence and figured out any disguises he wore in the end. Despite the rivalry, they could team up and work together when they had the common goals. Other than similarity with their faces, they are ones with secret identities and someone they want to protect. Their personalities were different and they were on the opposite sides of the law, the detective and the thief.

Kaishin is the most popular ship within the fandom. On AO3, Kaishin is the most written ship for both characters, and for both the Detective Conan and Magic Kaito tags. ShinRan, CoAi, and Kuroba Kaito/Nakamori Aoko are notable rival ships for Kaishin. There are over 2,800 works for Kaishin on AO3.

Fandom
FAN FICTION

DETECTIVE CONAN WORLD
 * Kudou Shinichi and Kuroba Kaito page on DCW

Trivia

 * Kaito and Shinichi are canonically almost identical, They also share a voice actor (Kappei Yamaguchi).
 * Shinichi's mother trained in the art of disguise under Kaito's Father, the former Kaito Kid, and their families were friends. Shinichi’s father and Kaito’s father were also had the similar rivalry. Although, it was never stated if Kaito and Shinichi had met before the events of the series still.
 * Kaito and Shinichi's voice actor has made an unofficial video about Kaito kissing Shinchi.
 * While it is only implied in the Manga that Kaito knows Conan's true identity, He outright states it in the movies
 * In Movie 3, Kaito has helped Shinichi by disguise as him when Shinichi almost told Ran that Conan and him are the same person, in repay to Shinichi helping one of Kaito's injured dove.