KaiShin

KaiShin is the Slash ship between Kuroba Kaito and Kudo Shinichi from the  Detective Conan/Magic Kaito fandoms.

Canon
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Kaito and Shinichi meet for the first time during the clock tower heist. During which, Kaito is attempting to steal the hands of the clock. Well Shinichi is in a helicopter up above attempting to stop him from doing so. They never end up meeting officially in this case, but they are both important parts of the story

Their next meeting is after Shinichi is poisoned, and becomes Conan. The Black Star Heist, Is their chronological first meeting, being earlier in the show than the Clock Tower Heist. In this episode, Kaito attempts to steal the Black Star, a pearl owned by the Suzuki Family. Conan, Currently living with the Mouri Family, Is invited to try and stop Kaito from stealing the Jewel, as his guardian, Mouri Kogoro, is a famous "detective". Conan manages to figure out where Kaito is, and confront him, setting off a firework in order to alert the police to his location. Kaito manages to escape though. He leaves a note stating that this was just a practice run, and that he will return to steal the pearl on a ship carrying the Black Star. When the day comes for Kaito to attempt to steal the gem again, He manages to get the upper hand to Conan, by disguising as his childhood friend, Mouri Ran, and when he's figured out, stating that he left her tied up naked in a boat.

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, and their families were friends. Its never stated if they had met before the events of the series still.
 * Kaito and Shinichi's voice actor has made an unoffical video about Kaito kissing Shinchi
 * Well it is only implied in the Manga that Kaito knows Conan's true identity, He outright states it in the Movies