Regret.
It happened every time. Some freak set of coincidences or some ridiculously elaborate plan would turn Edogawa Conan back into Kudou Shinichi. Heiji had been around or close by for every single one of these transformations, even when he didn't know it, and every time Kudou's time ran out, Heiji felt the same afterward.
Stomach-turning, ice-cold, heart-clenching regret.
The first time, it had simply driven him to find out more about Kudou Shinichi, to track him down and solve his mystery. But now the mystery was solved, and Shinichi was Conan, and Heiji had no idea if he'd ever see that confident smirk at its proper size again.
Sure, Conan was still fun to talk to and great to tease, but there was something that Shinichi's smile had that Conan's didn't. Shinichi's smirk had a magic and confidence to it. Conan's smirk was just a bit creepy. Funny how the same smile on the same person (technically) could look so different.
Every time that Shinichi disappeared and Conan returned, Heiji knew there was something that had gone unsaid, that he should've said, and he berated himself for not thinking of it.
When he first met Kudou, he thought it had been, "Where did you disappear to? What are you involved in?" or something like that - the type of questions a detective asks when he wants to solve an interesting mystery. But that wasn't it, because Conan was the one who answered those questions.
After the spectacle that was the Teitan High school play, Heiji thought it must be, "How long do you intend to keep this up?" - a question from a concerned friend to a troubled one. But again, there was nothing stopping him from asking that of Conan.
It wasn't until the third time that Conan had changed back into Kudou that Heiji realized what it was. They were working on yet another murder case on the freeway, on the way back from East Okuho when Heiji happened to glance over at Kudou. Shinichi was surveying the cars that had been stopped, his face just barely shaded from the glare of the streetlights by the cap he'd stolen from Heiji. Kudou's eyes glinting with the light of an unsolved case, and he was smiling a very familiar smile, one that Heiji hadn't gotten to see for months. The smile that he had fallen in love with.
And that was when he figured out just what it was that he had never said to Kudou Shinichi.
A/N: Well, I hope you liked this fic. I wrote this and one other short fic for a friend's birthday - she turned 18 on February 9. You can probably guess what her favorite pairing is. xD
Disclaimer: I do not own Detective Conan or the characters thereof. It all belongs to Gosho.