HeiShin

Heishin is the Slash ship between Shinichi Kudo and Heiji Hattori from the Detective Conan fandom.

Canon
Heiji and Shinichi meet first in Manga File 518, Heiji Hattori vs. Shinichi Kudo: Deduction Battle on The Ski Slope. In which they both try to solve the murder of an actor, at a ski resort they are both at. This case is a flashback, In which Heiji is telling Conan about a detective he met, that was better him, back when he was in middle school. What Heiji dosent know is that the mysterious detective was Shinichi. Conan realises this as Heiji tells the story, but does not tell Heiji that it was him.

Heiji and Shinichi meet again in Heiji's introductory chapter, Manga File 92, The Great Detective Of The West. This is after Shinichi has been poisoned and turned into Conan. Heiji shows up at the Mouri Detective Agency, looking for Shinichi. He deduces that Shinichi must be watching Ran from somewhere nearby, since he never asks how shes doing when he calls her. He also gives a sick Conan a strong chinese liqour, Pikaru, as a cure to a cold he has. As Mouri gets a case, Heiji decides that this case would be a challenge between him and Shinichi. As Heiji and Conan try to solve the case, Conan gets sicker and sicker. Until he collapses, and Ran carries him off to another room. Then suddenly, after Ran had come back to the scene of the crime. Heiji claims that he knows who the suspect is, and accuses him of being the murderer. When suddenly, Shinichi appears, back in his actual body. It turned out that the Liqour that Heiji gave Conan, worked as a single use temporary antidote for the poison Shinichi was fed. Shinichi figures out who the real culprit is. Then Shinichi and Heiji have a conversation, where Heiji says that he lost the compition, Shinichi responds with, "There's no win or lose, good or bad in this business… because there is always only one truth." But suddenly, Shinichi begins to feel himself turning back into Conan again, and he runs away.

Heiji and Shinichi run into eachother again in Manga File 117, The Holmes Freak Murder Case. Conan entered a contest to win a first edition Sherlock Holmes book. He convinces Ran and Kogoro to Go. When they get there, it turns out that Heiji signed up too, because he thought Shinichi would be there. Everybody is given a test on Sherlock Holmes to complete. Later on, the host of the event is killed. As somebody made his car fall off a cliff well he was asleep. Heiji and Conan try to solve the crime, well Heiji starts to notice that Conan does not act like a normal child. After another person is killed, and somebody else is stabbed in the arm with an ice pick, Conan figures out who the murderer is, and uses his Stun Gun Wrist Watch to knock him out, and then uses his Voice Changing Bowtie to mimic his voice, and pretend he solved the case. What Conan does not know is that Heiji woke up halfway though his deduction show, and pretended to be asleep. After everybody else has left the room, Heiji confronts Conan and accuses him of being Shinichi. After Heiji threatens to tell Ran, Conan agrees to tell Heiji how this happened to him. This leads to Heiji and Conan developing a strong friendship for the rest of the series.

Fandom
Heishin tag on Ao3https://archiveofourown.org/tags/Hattori%20Heiji%20*a*%20Kudou%20Shinichi%20%7C%20Edogawa%20Conan/works