Obligatory spoiler warning.
Trucy Wright
Assistant + Close Friend
Although they've only known each other canonically for a few months, they're pretty close. Their friendship definitely has an older brother-little sister dynamic, what with Apollo being a worrywart and looking after her in Phoenix's absence. Their personalities compliment each other well, and Apollo definitely works better when Trucy is around to be his sounding board and to lighten the mood.
Things have gotten a little awkward with the whole "hey, you're siblings" revelation, but it's more because Apollo is sort of working through that. Though honestly it explains a lot.
Phoenix Wright
Awkward Lawyer Buddy
This is a really complex, awkward sort of relationship. First of all, he's actually meeting the Phoenix he was such a fan of, and it's a little weird. That's partially because he didn't realize what a dork Phoenix was. He's just so young and not quite as competent as he seems in court.
The other part of it is that he knows Phoenix in the future, and he's so different from the Phoenix in Route. Apollo has to reconcile two contrasting images of someone. Plus, he comes from nine years in the future, and he has to keep a lot of secrets from Route!Phoenix.
Miles Edgeworth
Traveling Companion
Apollo likes Miles, even if he can be a little frustrating sometimes. But he supposes lawyers have to be stubborn to get by. Somehow he's not as bothered by meeting the child version of a very famous prosecutor, but that's probably because he's never personally met Edgeworth.
He does fret a bit about Miles, since Miles doesn't act very much like a child. Plus Apollo, being the future-boy he is, knows some of the demons weighing Miles down.
Remi Altava
Logic Buddy
A lady full of common sense and wit. Apollo likes her logical mindset and her pleasant personality.
Kay Faraday
Justice Buddy
She's a little strange, though honestly he's met stranger. Apollo thinks she's a nice person in spite of her weirdness. He does still wonder why she feels the need to recite speeches from really high places (because who likes heights? Yikes).
Larry Butz
Friend of a Friend
Miles called him an "unreliable-looking person" and Apollo is inclined to agree. Larry's a nice guy, but he can be a little overemotional and hard to understand. Though Apollo thinks he's a good guy, considering how much he's helped not only Apollo but also Phoenix out.
Klavier Gavin
(Mostly) Friendly Rival
Ye olde rival from L.A. Typically, Apollo is on friendlyish terms with Klavier, but the arrival of Kristoph sort of threw a wrench into all of that. Apollo appreciates his dedication to justice and truth. However, his diva fits are frustrating and he can definitely be a glimmerous fop. Apollo is also sort of jealous of Klavier's cool factor.
They're not on great terms, since Apollo tried to argue that Klavier didn't understand the real situation with his brother. Right now, he's a little worried about how Klavier is doing.
Kristoph Gavin
Nightmare Fuel
Apollo's batshit insane ex-mentor. Apollo both hates and is afraid of Kristoph. Everything Kristoph did is sickening to Apollo, from the coldblooded murder to the way he manipulates others. He is indeed the devil. Kristoph's nice guy act is just irritating Apollo, though he recognizes that there's not much he can do about it. He just wishes more people believed him about Kristoph.
Machi Tobaye
Former Client
One of Apollo's former clients. He did do some bad things back home, but Apollo thinks he's a good kid deep down. After all, smuggling is nothing near as bad as murder, and he was influenced by an outside force. Apollo hopes Machi will get the second chance he so dearly wants here.
Ema Skye
Scientific Detective
A Snackoo-munching, science-obsessed detective from back home. Apollo really doesn't like catching Ema when she's in a bad mood (and he doesn't like being the cause of her bad mood even more). But when she's in a decent mood, she's a really helpful and even a little nice. Her dedication to science is admirable (and really helpful when it comes to trials), and he helps her out with some of her experiments. Though he could do without having Snackoos thrown at him.
Heather Mason
Acquaintance
A kind of weird, excitable sort of person. Although she had a brush with the law, Apollo's been willing to give her a chance and it's paid off so far. She definitely has an interesting way of wording things, and she seems like the sort of person who doesn't take crap from anyone, which he has to respect a little. Apollo never wants to end up on her bad side, though. Right now, they're casual acquaintances.
The Doctor (Eleven)
Acquaintance
He's a complete weirdo, going on about the majesty of humanity and blue boxes. But Apollo does sympathize with his worldview-- both of them think that murder is wrong under any circumstances. In a way, he has to respect the Doctor for that, even if he's a cocky, frustrating person sometimes.
Cocona Bartel
Acquaintance
Cute and easy to talk to. She's a good sounding board for theories and she usually has some useful information for him. Apollo thinks she's a nice girl, and they have the potential to be good friends.
Professor Layton
Acquaintance
Apollo's puzzle buddy. The professor seems sort of like that kindly uncle you see in fiction. He's a logical, friendly person which is Apollo's favorite kind of person. Apollo would love to hang out with the professor and his friends at some point, probably when Johto stops being failtastic for him.
Iris Fey
Acquaintance
A lovely, sweet girl who has the misfortune of being lumped with her batshit sister. Apollo thinks she's kind of cute (which is probably why he's so easily flustered around her). Apollo helps her out when he can, though he's surprised at the unexpected strength she showed during that whole Dahlia-poisoned-Phoenix event. He has to respect her a little for that.