Shinichi's friendship with Hattori Heiji is SO important to me.
Like, up until now in the manga we see him around Ran, who's his best friend, but... she's also the one he has a major crush on, and she's a girl, and the series is still early on so teenaged boys, no matter how nice, are kinda sexist. Other than Ran there's Sonoko, who's more Ran's friend than his, and his teammates in the soccer club. There's also Agasa.
Except... as said, Ran's his crush, Sonoko isn't his friend (they don't exactly get along much at first), his teammates in soccer only really play sports with him, and Agasa is much older.
Then he shrinks, and he has... well, he so far only has Agasa he's telling the truth to. And he has the Detective Boys in school, but they're little kids he's babysitting almost. His relationship with Ran is strained by lies and how she's treating him as a kid (and she has to), and he's unable to talk to anyone he knew from high school.
Enter Hattori Heiji, who is not only his own age, but someone who can keep up with his reasoning as he's coming up with things - not just after he's started to explain it all. And when he becomes someone In On The Secret... as much as we make fun of him for messing up with "Ku- Conan" all the time, I see it as kinda important, in a good way, too - because it proves that at no point does Hattori looks at him and sees "Conan" first before he sees Kudo Shinichi.
To Hattori, he is always Kudo Shinichi.
He respects him fully when he's shaped like a child, and Shinichi knows that Hattori will continue to treat him the same once he's returned to his normal body, too.
I've seen so many takes on how both Hakuba and Kaito deal with the aftermath of Nightmare and the Dark Knight heist.
Chronologically, this actually takes place after they've both appeared in Detective Conan cases, so that means Kaito's dealt with at least two cases in which murders have taken place already. That said, this is different; someone's tried to take advantage of him as Kid/used Jii against him, and when he was figuring out how to get out of the situation the man's son (shown above) distracts him and causes him to fall.
The big thing here is that Kaito is directly responsible for having tried and failed to save someone on one of his heists, and he was clearly distressed when having to make the call to shoot the mask off the man's face so that his son wouldn't realise his father was the bad guy he'd been chasing.
And since Kaito isn't a criminal detective like all the other Gosho boys are, it hits him. Hard. It wasn't even his fault, but I can see him blaming himself - and I've seen people have Hakuba being sympathetic to him after this, because as shown in the panels above, he knows what likely happened, and that as much as Kaitou Kid is a criminal, he never wanted anyone to die.
It's honestly one of the big reasons I'm salty that Hakuba's not in Japan much after his first main appearances, because having him continue to attend school with Kaito and there be this thin line between "detective who wants to catch him and put him in jail" and "friend, who happens to know/has figured out his secret identity and who because of that knows when something is off with him and will give him shit for it or give him space when he needs" is SUCH a good dynamic that they miss out on by having him be absent.