The moment Ippo wakes up after his very first spar with Miyata to find out that he was accepted at Kamogawa Boxing gym, Sendo continuing to fight even when he was unconscious in response to the cheers of his supporters and Featherweight Champion Date Eiji symbolically handing the baton to Ippo when he retires. Even Coach Kamogawa's backstory can move you to tears.
Just look at the friendship forged between Ippo and the bullies who used to pick on him. At first it looks like they just become fans because as a boxer he must be strong, but as time goes on, not only are they fans, but quite obviously his friends.
Shortly before Ippo's first big “A-Class” tournament, his mom fell ill due to overworking. This, of course, leaves Ippo with a huge, heartbreaking choice. And, if things stay the way they are, will force him to quit boxing. Then in comes Umezawa, head of said bullies. He berates Ippo for not asking for his help in the situation, asks to work at the fishing business, and even tells Ippo he quit his other job because "he wanted to follow his heart for once." Then, after a first few incredibly hard days (and the realization that all days are like this), one where he almost gave up, he came back the next day anyway. If that doesn't show how true the friendship is, nothing will.
After Ippo's brutal title defense against Sawamura (which results in Ippo needing to recover), Umezawa decides it's time to move forward with this life and pursue his own dream- being a manga artist. He's spurred on after Ippo and the boxing gang end up enjoying it (so much so that they tear a few pages fighting over reading it). To follow his dream, however, he needs to quit working with Ippo and Hiroko so he can devote his time and energy towards it. Before he does, however, he decides he needs to come clean with Ippo's mother about the fact that he used to be the leader of the bullies that beat Ippo up. He attempts to confess, but before he reveals it Ippo gets up and tells him to stop, showing he doesn't care about it anymore. Hiroko, on the other hand, tells him he needs to hold his head high to the future, showing that she knows he's a changed, good person, and shouldn't linger on the past anymore. Ippo shouts his parting words as he and Hiroko set off for the day:
Ippo: Umezawa, your manga was awesome! You can count me your first fan, just like you were mine! And remember, we'll always be best friends!
Perhaps just as sweet- Umezawa makes sure to call Itagaki and tells him to help out at the fishing shop, ensuring that Hiroko doesn't suffer from overworking while Ippo is recovering.
Ippo's relationship with Hiroko, his mother, has been heartwarming ever since episode one. A specific example of this is the conversation Hiroko has with Alexander Volg Zangief after their match, which leaves Ippo comatose for a few days. When Volg asks her if she wasn't worried about Ippo's condition, she says she lost her will to complain after seeing Ippo work so hard.
Hiroko: "Whatever it may be, seeing your son work so hard, is a wonderful thing for any mother."
Even very early on in the series, before Ippo even joins Kamogama Gym, Takamura gave him a week to catch 10 leaves with a jab. After practicing late one night, he oversleeps and misses out on helping his mother at work in the morning. She leaves him a meal and a note saying that while she doesn't know what he's been so absorbed in the past few days, she's just happy to see her son being happy and full of spirit, and encourages Ippo to keep doing whatever it is and not to worry about her.
After suffering his first defeat at the hands of the, at that time, Japan Featherweight Champion Eiji Date, Kimura, Aoki and Takamura head to the locker room to cheer Ippo up. Aoki and Kimura, anticipating that Takamura will be a Jerkass and put Ippo down for his first lost, reprimand Takamura and tell him not to do anything that will worsen the mood. Upon entering the room, everyone holds their breath, expecting Takamura to lay it into Ippo, but he simply pats him on the shoulder and tells him he did a good job.
Turns into a Crowning Moment of Funny when he backpedals after everyone gives him an odd look showing that they weren't expecting that, says exactly what everyone thought he was going to say and is immediately whooped by Coach Kamagawa and thrown out of the locker room.
After Itagaki's despressing loss in his debut match, the kid does't show up for a few days. In that time period, Ippo asks Takamura (now set to take on the World Championship) why he continues to box as the group does roadwork. Takamura claims it's because he wants to keep showing he's the strongest, but inwardly he admits that he's comfortable in the ring and with everybody else at his side. To that end, he throws his towel to everyone and tells them to wipe their faces- his intent is to take their sweat and effort with him when he gets in the ring. It's at that moment Itagaki returns, adding his own to the towel. Nobody says a word about his loss, just happy that he's come back to join them. While it's broken up with brief moments of hilarity regarding Aoki's eyebrows, it really shows how all of them, even the new kid, are about as close as family.
Takamura finding the strength to keep fighting against Bryan Hawk, realizing his coach and his juniors all support him- thinking about them is the only thing that keep him standing upright at one point. The entire time, Coach Kamogawa is torn, feeling utterly helpless and incompetent, incapable of helping Takamura strategically. When the round ends, this exchange takes place-
Takamura: I... I went down. I went down hard. Really.
Takamura: If I didn't have support, I couldn't have remained upright. You've always supported me... I understand now...
Announcer: Seconds out!
Takamura: Well, then... [gets up unsteadily, ready to fight]]
Kamogawa: Your mouthpiece. [Holds it out]
Takamura: [Stares at him for a moment with a smile- then limps over to him and gives him a one-arm hug, leaving Kamogawa at a loss for words] You're... you're the best second ever.
Volg's return in the manga to Japan to get his Boxing gloves is one giant moment of fluff as Ippo and he get along fantastically, as he stays with Ippo and Hiroko for a few days. He leaves begrudgingly knowing that being there in Japan was "too warm and kind", and that if he didn't leave then, he'd never want to go. It becomes a Tear Jerker when he asks Hiroko to say "I'll pray for your success son" in Russian in his dead Mother's place, and responds "Thank you Mother". He leaves without saying goodbye to Ippo, but knows they already had their own kind of goodbye from their spar, telling Umezawa they'll meet again one day, in the ring.
After Ippo's title defense against Sawamura Ryuuhei, Sendou goes to check on Sawamura as "we're technically friends," which is heartwarming in itself. Unfortunately, the beatdown was so bad that Sawamura has to go into surgery, but Sendou still sticks around. Sawamura's only other friend, his former teacher, says he hopes his defeat will teach him a lesson about hard work, and that he's not alone; sure enough, Ryuuhei tells Sendou he wants to continue boxing, at which point Sendou offers a brief but inspiring speech about what he sees in Ippo:
Sendou: It's weird, ain't it? Even after getting beaten up so badly, you still want to keep on boxing. Something about Makunouchi always makes you feel that way. His fists weren't honed on the streets, like ours. His were built in the gym. It makes you think you can win if you train harder, that you can grow stronger. His fists carry that message with every punch. So you think, "I'll train, come back stronger, and beat you." He makes you feel that way. Our fists are murder weapons, designed to put a man on the ground, so he never gets back up. But Makunouchi's fists just make people want to fight harder. His fists pick you up.
Shinoda finally getting praised by Kamogawa - especially considering Shinoda feels like his methods of training are dragging Kimura and Aoki down. The poor guy nearly cries and gets all happy that the Coach finally said what he did.
Mashiba's return match after his suspension counts—in a very weird and Mashiba like way. In the year he was suspended, his boss at work put together a Mashiba fan club and cheering section, which Mashiba himself seems to find completely irritating. But, whenever his opponent would sneak in a foul (as tends to happen in his fights), putting him into his old bloodlust, he'd hear their cheers, and would fight back clean. Somehow the final shot of him holding up his belt and angrily yelling "You happy now!?" at his cheering section just brings a smile to the face.
The final four episodes of Rising, which covers Kamogawa's past with Nekota. More specifically, the ending of that arc with Nekota leaving with Yuki back to his hometown in the mountains, while Kamogawa makes a promise that he'll train a boxer to reach the world.
Doubles as a tearjerker too, in the final episode. After the credits roll, we get a message dedicating Rising to Kenji Utsumi and Ichirō Nagai. Very significant, as the two are not only the respective voice actors for Kamogawa and Nekota, they both passed away (Utsumi in June 2013, therefore having to cast another VA for Kamogawa, and Nagai in January 2014).
After a thousand chapters, Mashiba finally accepts Kumi liking Ippo back.
The crowd reactions to Ippo's returns from his losses. The first one was after 5 months and the crowd roared when he enters. The roar was even bigger the second time around, which was after 10 months, showing that Ippo is truly one of the most beloved boxers in all of Japan. It's just really sweet to know how beloved this guy really is.