The end of the arc when Mitsui finally rejoins the team. The build ups on his past, his descent to be a Delinquent, and culminating on him eventually trying to destroy the club and gets severely reprimanded by... Kogure, in which he spouts off a lot of truth. And then there's Anzai coming into the gym and all of Mitsui's flashbacks come off together. In the end, Mitsui eventually fell to his knees, crying and said to Anzai: "I... I want to play basketball..."
Another of the biggest tearjerkers in the whole series is Sakuragi being reminded of his biggest failure... saving his beloved father's life because he was beaten up by the bullies that were threatening him in his way to the hospital. "My father... he had a heart attack.. JUST LET ME GO!" For a show that has lots of sports action and comedy, it has a surprising dose of Character Development.
It was nice of Akagi at the end, too. Rather than getting pissed at Sakuragi for making a mistake, he recognized that it was an honest mistake on both his part and Sakuragi's, and even gave our red-haired Idiot Hero a Cooldown Hug as he cried over the team's loss. Yep. Sakuragi wept like a child and Akagi comforted him. Crosses over as a CMoH considering their usual dynamic.
Along with a combo of Heartwarming Moment, there's also Uozumi's past. To wit, he actually started out completely untalented and was constantly scolded for low stamina, bad skills, etc. It was so bad that Uozumi nearly gave up basketball, but then the now-Coach Sergeant Nasty Taoka... rather than scolding him like usual, just sat down calmly and then gave a heartfelt talk on how he's actually thankful that Uozumi is in the team and encouraged him to move on. As a result, Uozumi is able to keep up and eventually become one of Ryonan's top players and is the feared 'Boss Monkey' we all know and love.
Also a Heartwarming Moment, tell me you didn't cry when Sakuragi got up and said: "I love it, and this time I mean it."
Anzai-sensei's last days as the "White-Haired Devil". His star student Yazawa got fed up with his harsh methods when Anzai just wanted to shape him to be the best Japanese basketball player, culminating in transferring to America. When Anzai got a video on how he's doing, he realized that Yazawa's basic skills are kind of lacking and his teamwork didn't fare so well with the other American players, despite the other Japanese praising how impressive he became. Anzai's attempts to call him back was never responded and the next thing he heard about Yazawa was that he died due to car crash, rumored due to stress. All because he's being the "White-Haired Devil" to the end.
To drive the nail home, when Anzai visited Yazawa's grave, his wife gave him one last unposted letter of Yazawa. Instead of cursing Anzai for his harsh methods, Yazawa was apologizing and expressing how his teammates in Japan also rarely passed the ball to him. He decided to go to America as a method to thank Anzai for all he taught and hopes to jump to his dreams (which he tragically failed to do). This soul-crushing event was the last straw that Anzai quits the college coaching and becomes the "White-Haired Buddha".'
From 10 Days Later, Haruko's letter explains that Akagi's scholarship was rescinded after losing the nationals, so he had to study for entrance exams like anyone else. Last we hear about him, his grades are falling and he seems to be in a slump, because he misses basketball that much.