Isamu will come in contact with a lot of people while in game, so listing all of them here would get crazy. Those that get a mention are ones who've had a significant impact on him in the course of play. One little chat might not cut it unless he takes particular interest in the subject.
Friends
Kashima Naoki (
denyingreasons)
A friend from back home. Naoki is the person Isamu trusts the most in this place, even if his friend doesn't remember supporting his Reason. He's WAY too caring for his own good, but Isamu finds he doesn't mind having someone around to worry about him or to worry about in return.
Recently, he's been coming to terms with the fact that he'd be kinda lost without Naoki's help, even if he thinks he's being more like a mother sometimes than a friend. In fact, he can be a little possessive of him, as seen in the dilemma with Richard. All three live in the same house now, though, and he's about as close to them as he can get without actually being involved with them. That should disturb him, in a way, but it doesn't.
Richard (
windol_prince)
Richard was originally the cause of a lot of trouble for Isamu. He and Naoki got into a relationship, and that left Isamu feeling like the third wheel. Worried that his best friend might abandon him for this man (oh the irony), he became increasingly jealous and eventually did something he regretted. It took some reassuring from Naoki, but he finally got over his worries.
The three of them are something of a trio now, having moved out of their respective apartments and into their own house, and they've all become rather dependent on each other. (Richard is as much of a troll as he is, which is unfortunate for Naoki.) He's also vowed to take both of them back to his own world, which is something Isamu's still unsure about.
Hamato Raphael (
gaijin_ninja)
Isamu got involved with Raphael on account of his own boredom. What started out as a dare to the turtle to keep a pet spider despite his arachnophobia dislike of bugs eventually led to a request for training. Isamu's attempts to find something to do with himself might have a positive outcome, but he's going to be hurting before it gets there.
Aside from Naoki, Raph is really the only one he feels he can confide his problems to. (And there are some things, that Raph's the only one he'll share them with period.) He's gotten over the strangeness of having a turtle for good pal, for the most part, but that doesn't mean he won't tease him when he has the chance. The two of them are both good for each other and terrible for each other at the same time.
Sanji (
oda_hates_me)
Sanji is someone Isamu respects, a position that's difficult enough to achieve. He's a good friend of Naoki's and despite the fact that their personalities clash pretty hard, he's found himself wanting to be friends with the guy. (It doesn't hurt that the chef's helped both of them out more than once.)
He doesn't hold the incident with the A.I. against him, not after everything else the Malnosso has put them through. He's one of the handful of people Isamu trusts in this place, and it's a good thing they don't live that far from each other anymore, as that means he can run to the Strawhats in a time of need. And he has.
Good Acquaintances
Hamato Donatello (
i_speak_softly)
Raphael's brother. He seems like a decent enough guy, and he's been helping Isamu with his bo staff training. Though he's a bit of a know-it-all, there really isn't anything to dislike about him. He's also currently the only brother Raph has left in this place, so he'd rather see him remain safe in Luceti.
Usopp (
sniperkingftw)
As both an aquaintance of Naoki's and a Strawhat crew member, Usopp gets bonus points right off the bat. He's a bit odd, but also easy to troll, which makes him worth talking to.
His rescue of Isamu when he was being attacked by the AU versions of his friends helped bump up the teen's opinion of the pirate considerably.
Ted (
300yrswandering)
NAOKI HAS STRANGE FRIENDS, but anyone who's willing to stick Naoki in a dress as a good natured prank can't be all that bad. He also seems to be a fellow troll, which is both a fun thing and makes Isamu feel kinda bad for Naoki at the same time.
Ginko (
one_green_eye)
This guy's kind of odd, but he's friends with both Naoki and Sanji, so he probably has some redeeming qualities. Ginko makes it onto the 'good' list only because he saved both Isamu and Naoki from mushi (even though Isamu couldn't even see what he was being saved from).
Neutral Acquaintances
Winry Rockbell (
wingsthatwait)
Some girl friend of Raph's that isn't a girlfriend. She's okay because she honestly cares about the turtle brothers.
After some awkward times involving her nearly becoming a prostitute during an event (though she claims that's not the proper word for it), he's actually been a little more pleasant toward her. Kind of. She can also make cool stuff.
Asbel Lhant (
raizanshou)
One might think that any friend of Richard's would automatically fall higher on the list, but this is Isamu. He just doesn't know the red-head well enough yet, though he seems like a friendly guy. If a bit of an airhead.
Nekozawa Kirimi (
lost_koneko)
At first, Isamu was just kind of messing around with the kid, but let's face it... she's adorable. She's adorable and Isamu has a gooey center somewhere under all those layers of "jerkface". So maybe, just maybe, he'll try and actually give her a few helpful words now and then.
Enemies
none currently
Memories
(Characters that have been dropped.)
Rubi (chisoku_outlaw) - Naoki's former roommate. Isamu found him rather stoic and uninteresting, but Naoki seems to think he's worth hanging out with. (Then again, Naoki would probably hang out with most people.) To his credit, Isamu wasn't as much of a jerk to Rubi as he could have been.
Lillia (friendofspirits) - Who is this chick? No seriously. She's worse than Naoki when it comes to seeing the best in people, and that's saying something. Isamu met her on what was apparently her first day here, and she thought nothing of his rather rude greeting. In fact, she actually believed he was a good person, something he found utterly baffling.
Hayasaka Chiaki (powerfulbeauty) - Chiaki used to be a friend, but while in the Vortex World, she, him, and the other human survivors became twisted in their desires to see their Reasons made reality. In most endings of the game, Naoki would be responsible for stopping and killing Isamu, but in the Musubi ending he's taken out by Chiaki before Naoki reaches him. Thus, this is what he remembers here. Though he attempted to converse with her naturally, he's honestly scared to death of her.
Kuzuki Kakyou (yumemi_kakyo) - Another friend of Naoki's. This one can apparently visit the dreams of others, which Isamu found to be no small breach of privacy. Aside from asking a couple nosy questions, however, he was generally polite. Isamu even performed a bit of healing on him after he was wounded by Moro, despite not wanting anyone to know he'd been working with Nala.
"Alice" (maybealice) - Isamu ran into this guy more than once, and he's still not really sure what to think of him. He was helpful enough, and was someone to flee from evil world-destroying beings with while in the Closed Space, but he was never really able to form much of an opinion on him. Mostly, he just found him a little strange.
Suzumiya Haruki (god_is_a_dude) - Apparently, this guy was Naoki's boss. Or something like that. Isamu gave him props for being able to make Naoki dress up in funny clothes and hand out pink fliers. At the same time, he kept an eye on the guy. After all, he doesn't like anyone who gets to boss around his friend more than he does.