Early on, Kei and Rin dragging Obito to the hospital after seeing how badly he'd been hurt by bullies. Kei wants mostly to hunt them down and end them, but Rin manages to talk the other two into just making sure everything's all right.
Another early moment, but the ending of Chapter 13. After Wataru's passing, it takes a week for Kei to emotionally recover and return to the Academy, only to face Obito and Rin again. The resulting conversation really tore at the heartstrings because it solidified the trio's bonds of friendship right then and there.
Obito: "Oh Kei. Rin-chan...?" Rin: "We're here to support you, okay? If you need anything, come to us." Kei: "Thanks, Rin-chan, Obito." Obito: "You're going to graduate with us, right?" Rin: "Obito!" Obito: "I'm serious! If you graduate with us, we'll look out for you, okay? No one will ever, ever say anything bad about you or your dad while we're around! That's a promise!"
Speaking of the hospital, the Chunin Exam Arc also features one. After Team Minato is swept 0-3 in the prelims, Kei is in the hospital. Kakashi pops in for a late-night visit at one point and shares an apple with her.
Hayate in one of Lang Noi's sidestories. His response to being told Kei is a jinchuriki?
Hayate: She's afraid I'm going to hate her-it's just so obvious. That's even more obvious than the not-human chakra right in front of me, in some ways. And it hurts, too, because I can't imagine being that scared of my own sister.
Then he hugs her and asks if Isobu is hurting her. After being told that she's fine, he then wonders what the problem is.
The ending of the Missing Scene/Side Story starring Kei's Mom, Miyako. After all the bloodshed that the reader had to see in the side-story, ending it with what appears to be the most adorable first meeting between Wataru and Miyako really gave the feeling that everything was going to be okay. Miyako wasn't going to be alone anymore.
Wataru: "May I ask you about your katana, stranger?" Miyako: "My sword?" Wataru: "Yes! Even from here, I can tell the balance is beyond perfect. And is that genuine shark-skin for the wrap?" Miyako: "It's not for sale," Wataru: "I don't want to buy it! I just want to bask in its glory. Because this weapon is glorious." Miyako: " It's a katana." Wataru: "Do you have any idea how shoddy modern mass-forging can be? Maybe you don't? I've snapped a blade or two and I've never been a kenjutsu specialist. That shouldn't happen. Please, tell me your name, o vision of moonlit kenjutsu mastery." Miyako: "..." [surprised, baffled face] Wataru: "Um. Maybe I should introduce myself? Wataru Gekkō, of Konohagakure." Miyako: "Miyako. Of wherever." Wataru: "Well, Miyako-san, I'd really like to pick your brain about swords. I've used a few, but you're probably better than I am if that's your primary weapon, so Please?" Miyako: "It would be acceptable."
This would later be turned into a Tearjerker considering what happens to Wataru when Kei is 8.
In chapter 96, when Kakashi comforts Kei after her major breakdown and revealing to him and Minato that she's a reincarnation and (implicitly) admitting that she thinks she shouldn't have been born in the Naruto-verse.
Kakashi: "No matter what you think, I'm glad you exist. Not your prophecies. Not your power. Just you."
Gai is a sweetheart that went around the village collecting get-well wishes for Kei, on top of making the cards himself and getting her a present.
Rin and Obito tell her how much they value her, in the midst of a group hug.
Kakashi and she have a heart to heart talk that takes a burden off her shoulders.
Minato apologizes for the lead-up to the Memory Arc, and the kids are sweethearts, the lot of them.
When Kakashi gets the White Chakra Saber back as a birthday gift from Hayate and Kei in Chapter 109. It was one of the many losses from the Kannabi Mission, but it's his reaction that sells it.
Kei: The next thing I knew, Kakashi wrapped both arms around me and then I was trapped in a steel vice clamped around my shoulders. Momentarily stunned speechless, I lifted my arms and returned the hug more out of reflex than conscious thought, and Kakashi's spiky white hair brushed my ear as he hooked his chin over my shoulder. And while his fingers dug into my back a bit, I felt him start to shake. I leaned my head against his right before he buried his eyes against my shoulder, and the first tears finally snuck through his normally-ironclad self-control. Instead of squeezing harder, I just let my hands rest against his back. He'd take a minute and then he'd be okay. Everyone deserved a chance to cry from joy.
Chapters 115-116, where Kei finally realizes that Kakashi loves her.
The way the long-awaited reveal was handled warmed hearts, because even when Kakashi was unconscious, Kei watched over him.
Also, the first kiss, hands-down. It wasn't perfect in fairy-tale standards, as Kei can attest to, but it certainly didn't disappoint.
Kei: I kissed him. I caught him by surprise, so it wasn't a classic fairytale "true love's kiss", like in the movies. His mouth was open, so I felt our teeth hit and it wasn't a great first impression. Somehow, it was fitting that my first kiss would be a fumbling rush job. But it got better.
When Isobu realizes he's in the middle of the real ocean, he's immediately concerned that Kei is nowhere to be found. Once he confirms Kei is all right, he goes back to frolicking in the ocean and having fun, and Kei gets to witness what she calls the Great Belly Flop Tsunami from the crown of a palm tree.
Kei takes the time to drag the displaced sharks back into the ocean afterward. She's not a fully-fledged Friend to All Living Things, but she does good on occasion.
After exploring the island and the sea around it, Kei and Isobu take a second to reaffirm their bond.
Kei: "Youre the best survival buddy anyone could ask for." Isobu: I did say we were partners. That will not change even if you are preoccupied with your problems. Kei: "You didnt have to say it like that, jerk. You were worried too." Isobu: And I will still be worried five minutes from now, an hour, or a day as long as we are in an unfamiliar place. But I wanted you to know that you can rely on me. Since you seemed to have forgotten. Kei: "Well, you know me. Im a slow learner that way. So, I guess we need a plan."
When Kei is about to go to sleep, she offers to stay awake and daydream up pirate movies for Isobu to enjoy. While Isobu declines, it's the thought that counts.
Within a ridiculously short time frame, Kei ends up being essentially adopted by the Whitebeard Pirates. Though they realize she's a near-stranger and her backstory is full of holes, her awkwardness, quirks, and willingness to help people wins them over. In typical Kei fashion, though, she isn't fully aware of the full scope for a few months after she leaves the Moby Dick behind.
Haruta: "Youre the biggest clumsy goof of a landlubber weve ever met, but youre our friend!"
Kei has a heart-to-heart with Thatch about things and people she's homesick for, including Kakashi, Hayate, and her students. Thatch plays off his end with a joke, but the two of them come to an understanding and he accepts her reasons for wanting to leave the Moby Dick. The moment is violently cut short, but after she helps save Thatch's life when Teach almost succeeds in murdering him to obtain the Yami Yami no Mi, she's definitely a part of the Whitebeards' True Companions. Kei even sticks around for an extra two weeks longer than she planned to make sure Thatch is going to be okay.
After she embarks on her journey to find the other jinchuriki and deliberately lets her boat get eaten by Isobu, she doesn't realize that Namur saw it happen and ends up mistaken for dead for a couple of months. When Ace runs into her again by accident, she's in disguise as a random pirate. Because he recognizes the boat she's been using, Ace threatens to charbroil the "stranger" unless "he" gives up information about what happened to Kei. When Kei drops the diguise and reveals that she's alive, Ace is overjoyed.
Isobu is used to people running away in terror whenever he reveals himself. Ace, after initial hesitation, introduces himself politely and strikes up a friendly rivalry over which one of them is going to kill Teach first.
The same acceptance also manifests in Luffy, who declares Shukaku a member of the Straw Hat Pirates almost as soon as he screws up his name for the first time. He later goes on to recruit Fu and Chomei together offscreen in the Skypeia arc, with exactly as much cheer.
Later on, Ace and Luffy's wholehearted appreciation of the Tailed Beasts as people ends up being the deciding factor in the Tailed Beasts collectively choosing to destroy Impel Down as retribution for the Marines taking Ace from them.
Gaara is a member of the Straw Hat Pirates by the time Kei meets him in Alabasta. He trusts Luffy enough to tell him bits of backstory that only Kei knows otherwise, and Luffy praises him as the best lookout ever. Despite a rough start landing in Loguetown, it's clear that Gaara is far happier here than he ever was in Sunagakure. He's even loosened up enough to give Kei a hug for a greeting, and Kei thinks that the Straw Hat Pirates are great for Gaara. She even dismisses the idea of bringing Gaara along on her and Ace's journey, deciding he's better off with Luffy's crew.
Upon meeting up, Isobu and Shukaku immediately start arguing and jostling each other like the siblings they are. They scare the Straw Hat Pirates pretty badly in the process, barring the Monster Trio and Gaara, but quickly start arguing over which of them is "older" and generally being brothers.
Though it's less present before they encounter Yugito, Kei treats Ace like a younger brother even before she acknowledges the whole "a Whitebeard in all but name" thing.
It's described by one reviewer as "A frazzled helix of mutual babysitting."
During all the occasions where Kei lets some of her past slip, Ace tries to either lighten the mood or empathize with what's happened. Kei, for her part, is highly aware of Ace's mood shifts (due mainly to being reminded of his past as Gol D. Roger's son) and tries her best to look after him despite being equally in the dark about his past.
Kei fully expects to get into a fight with Han, the same way she did with Yugito. Yugito is equally wary as they follow the man's trail to a tiny dairy farm (literally; the cows are miniature). Turns out that, no, Han is a Gentle Giant and has been babysitting the eight-year-old proprietor while her parents are away. He doesn't care for village-based hostilities or hatred. Talking him into getting a power boost is as easy as helping them out on the farm.
Han and Mona also help out when Ace shows up, having been hurled into a river for dine-and-dashing while Kei wasn't around to cover for him. They end up letting him stay in the farmhouse until he recovers a few hours later.
When Saiken first appears, he is frantic with worry about his partner Utakata. Having had a run-in with AdmiralAkainu while on minimal power that left him horribly burned, there's little question Utakata's injuries are life-threatening. Kei and Yugito put their hostilities aside immediately to help their fellow jinchuriki out, though they're both aware he might be really unhappy to see them when he wakes up.
Shortly thereafter, Naruto shows up and starts to work his magic on the resident downer. He starts by giving Utakata a nickname, is always asking for his opinion on things, and basically keeps being a little charmer where Kei and Utakata have too much baggage to speak civilly. By the time the group is out of Impel Down, Naruto is one of the few people besides Saiken who can hang out with Utakata when he's in a bad mood.
Over time, Utakata loosens up and starts participating in group goof-off activities. He makes bubble shows for the Straw Hat Pirates' younger members to admire, collaborates with Usopp to make a new bubble-based weapon, offers Boa Hancock romantic advice, drinks Whitebeard under the table in a Drinking Contest, and even goes with Yugito, Kei, and Naruto to a cafe during a bit of free time. He also acknowledges in his own POV segment that he genuinely loves Mei and is looking forward to being able to see her again.
Naruto greets Kei by tackle-hugging her right off her feet. Being one of Naruto's big sibling figures as he grew up really shines through.
He wants to know why Kei is wandering around the ocean with such weirdoes as Yugito and Utakata. Upon being told that they're working together to rescue a friend, Naruto immediately volunteers to help.
Right after that, Kei manages to get Naruto in contact with Kushina, and the two of them bawl their eyes out over their snail calls, because it's the first time in months that they've heard each other's voices.
Despite appearances and his general demeanor, Yang Kurama manages come across as a Grumpy Old Man with a goofy, back-sassing grandkid around Naruto. He still leaves the Revolutionaries terrified by his mere presence, but he's more willing to show a silly side than he ever has been before. He even interacts with his siblings without as much hostility.
Ace's POV reveals that the Whitebeard Pirates held a wake for Kei after her presumed death and "posthumously" adopted her as a fully-fledged member. When they found her again, Thatch ended up bawling in relief.
The Straw Hat Pirates all agree to throw themselves into the Impel Down break-in, despite having just barely avoided being arrested by Admiral Kizaru or pushed to parts unknown by Bartholomew Kuma less than 24 hours ago. Why? As Chopper says afterward, it's because Ace is Luffy's brother, and they're Luffy's crew. They know he'd do the same for them.
When Kei and Luffy finally make it to the bottom floor of Impel Down, they have no other considerations except to find Ace and bring him out alive. Jailors? They're dead men walking. Fellow inmates? Not important. Luffy is rushing around so much in an attempt to find Ace that he almost misses the cell entirely, only to ricochet back as soon as he hears Ace's voice. As soon as Kei rips the sea prism stone door off its frame, Luffy wastes no time hugging his brother and telling him that everything's going to be okay.
Kei, for her part, hangs back long enough for Jinbe to notice her before Ace does. Ace, having thought she was killed by Teach or otherwise unable to come after him, is stunned to find her helping lead the rescue mission. Practically his first question after realizing what this implies is asking after everyone else, current position in a cell be damned. And once he's freed, he hugs her.
Ace: (while hugging her) "Thanks for coming after me." Kei: (after he lets go) "No problem. I know you'd do the same for me."
As they make their escape, the group has to make use of the Reverse Summoning Technique in order to get out quickly. Ace, having experienced the nausea associated with rapid altitude changes, is not exactly happy about this.
Ace: "This shit again?" Kei: "Yes, because it's the fastest way out. No more stairs or running, just us on the outside of this pit." (holds out her hand) "Hurry up." Ace: [deep breath] " I'm ready." Kei: (teasingly) "You sure?" Ace: "Hell no." [smiles weakly] "But I trust you."
Ace and Kei finally have a chance to talk about why the Tailed Beasts like Ace enough to help out with (and then solve) the Impel Down situation.
Kei: "You know how long it took you to decide Isobu and the others were people worthy of respect? You treated him like a person within half a minute of meeting him." Ace: "Yeah, but" Kei: [pokes him to shut him up] "People back home still haven't figured that out, and it's been over a thousand fucking years."
Ace's narration: Though Ace would never admit it out loud, being this close to the biggest seafood combination he'd ever seen felt like one of the safest places on the sea short of the Moby Dick itself. When he sleepily felt Sabo and Luffy pile onto him, equally drowsy after devouring their portions of the huge breakfast, Ace just gave a contented sigh and fell fully asleep.
Ace finally gets an answer to the Trial Balloon Question he's been contemplating for the better part of a month. While out to sea and on Isobu's back, with Sabo there for moral support, Ace decides to let Kei in on his secret.
Ace: "What would you say What would you say if you met the Pirate King's son?" Kei: "If I met the Pirate King's son I'd raise my hand like this, then say 'Yo.' Just like I did when we met." Ace: "D-did you hear what I said? Gol D. Roger's son. People say the man was a demon! The World Government—they'd call anyone with his blood a demon just for that. It's the most cursed blood in the world " Kei: "Really? A demon? Then you're in good company, aren't you?"
Unlike almost all of Kei's other missions, Hayate can actually visit her and explore Tokyo at Kei's side. While he's The Gadfly, it's clear he still thinks the world of Kei. Obito and Kakashi also visit (the latter less often) through Kamui, meaning Kei's not nearly as isolated as she would be on a supposed solo mission. She even gets to act her age, and often.
In the first couple of chapters, Kei semi-intentionally makes a bad impression on her classmates, resulting in no one being willing to talk to her. However, on the day after the USJ incident, she runs into Hitoshi Shinso while shopping and ends up assuring him that she thinks he's a decent person, Quirk or no. Which is more than their classmates have been doing.
Though Hitoshi met Hayate not an hour beforehand, when the pair of them are cornered by villains who've taken Kei hostage, his thoughts run thus:
They both also talk Hitoshi through his panicked shutdown afterward and stick around until he feels better. All of this results in Hitoshi asking Kei to teach him how to fight.
Realizing her inadequacies as a teacher, Kei asks her friends for help. For a civilian kid they've never met. And they answer! Thanks to Gai, Kakashi, and Obito, she cobbles together a training regimen to help her friend get ready for the Sports Festival in time. Obito even volunteers to be a training dummy, since his intangibility power means he won't get hurt.
Kei also keeps a training journal of Hitoshi's progress. When his resentment of the hero students' progress gets to be too much and he starts tearing himself down, Kei makes a point of showing him to prove that others besides her have faith in his potential.
Team Minato reunites properly not long after the start of the story to go on anti-villain recon. After finishing, the three of them head to a bookstore for fun, like ordinary teenagers.
Despite knowing that Kei is a Child Soldier, Midnight takes her duties as 1-C's homeroom teacher seriously. She goes out of her way to show concern for Kei and tries to help support her emotionally, even if she can't do more. It's a fairly sharp contrast to 1-A's homeroom teacher, Eraserhead, who seems to actively dislike Kei and everything she stands for.
Hitoshi immediately notices when Kei gets brainwashed by Monoma's use of his Quirk. After snapping her out of it (and unknowingly saving the entire stadium from meeting an angry Isobu), he spends the rest of the cavalry battle doing everything possible to screw up 1-B's plan to get into the third stage of the Sports Festival. By the end, the only student from 1-B who makes it to the one-on-one matches is Shoda, who was on Team Shinso and thus gets a pass.
A minor thing, but Kei's influence seems to have softened Hitoshi's personality enough that instead of brainwashing Shoda and Ojiro, he actually talked them into joining his team.
After the Cavalry Battle, Isobu and Kei take the time to handle the anger that's been ratcheting up ever since Kei got briefly brainwashed. Isobu is in full Anger Born of Worry mode, and refuses to be soothed, but the two of them come to an agreement to leave the situation to Kei. Despite everything, they really are friends now.
Kei leads 1-C in cheering Hitoshi on throughout his tournament matches, and she also channels Gai for both Ojiro and Shoda. While 1-C is confused about the latter two, they accept her enthusiasm and join in.
Kirishima immediately shines in the Spirited Competitor mode, complimenting Kei on her fighting skills and accepting his loss once it happens with no resentment. Though she doesn't interact with him much, he's one of the friendliest characters in the story just from his few brief appearances. Kei immediately equates him to Gai and accepts the offer of friendship.
After Hitoshi defeats Tokoyami, his entire class erupts in cheers. Hitoshi looks away in pleased embarrassment soon after noticing that Kei is practically bouncing off the 1-C box's walls.
Homura, 1-C's class rep, takes it upon herself to try and mend fences with Hitoshi and Kei after effectively neglecting them like her classmates. While she isn't perfect at it, she negotiates the end to their Feud Episode by forcing them to talk to each other instead of just stewing. She even shows Hitoshi the second training journal, which Kei left for him in the hopes that space would give them time to cool off.
Hitoshi: "And I dont wantIve never had friends before, and I dont want to screw this up worse than I already have. Im sorry for everything I said. So, um Are we still friends?" Kei: "We were never not."
Hitoshi: "What? I"
Kei: "You heard me. One argument doesnt end a friendship."
In return, all of them get one step closer to a First-Name Basis with each other, changing honorifics all around.
When Obito and Kakashi are about to head back to Konoha, Obito pushes Kakashi into accepting Kei's hug.
Once 1-A realizes Kei is trying her best to avoid Bakugo, and that Bakugo's behavior is getting out of hand, they all decide to run interference between him and her.
Hayate finally explains that part of the reason he and Kei don't care about how "villainous" Hitoshi's Quirk might be is because his teacher is a mind-controller, and so is his entire family. The conversation eventually turns to family Quirks, and Kei lets Hitoshi know a little more about herself. While Hitoshi's upbringing means he doesn't understand the depth of the personal tragedy Kei's faced, he does his best to be a supportive friend.
When Hitoshi becomes Aizawa's apprentice, his emotions are all over the place. Kei talks him down and decides to help him celebrate this new, terrifying opportunity by taking him to a cat cafe. While there, they goof off with the cats and have a nice afternoon being ordinary kids.
During the Musutafu attack, Hitoshi runs after Kei without hesitation when she tries to rescue Izuku on her own, because he has no intention at all of letting her face everything out there alone.
Though they don't discuss it, Todoroki and Kei view each other as Not So Different—Kei realizes Endeavor is abusive, and Todoroki assumes that Kei's had a very rough upbringing. They both do their best to avoid each other's issues, despite being near-strangers, which ends up being the start of their friendship.
Todoroki and Izuku end up joining with Kei and Hitoshi's fight club, and they bring along Iida, Uraraka, and Yaoyorozu. More friends!
Kei and Yaoyorozu become friends through combat. As the author notes later, for some reason Defeat Means Friendship works for Kei in side-stories and not in her home universe.
While Hitoshi is wary of the idea that his and Kei's friendship might be subsumed or overwhelmed, he fits in with both the Dekusquad (which he coins) and is well-tolerated by Team Minato. Much later, when he brings up that their sparring buddy group is mostly made up of 1-A students, she assures him that Izuku's friends are their friends. And it bears out.
After All for One is found dead and Hitoshi gets some time to himself on an errand, he gets visited by Obito. In spite of some Anger Born of Worry because of finding out Kei's identity as Turtle, Obito smoothly takes Hitoshi's anger and gives him some good life advice. This later culminates in Kei texting Hitoshi once she's free to talk, and a promise to explain everything.
After the roller coaster that is the Hideout Raid Arc and all the revelations therein, Hitoshi and Kei are still friends at the end of it all.