During the National Finals Fuji finally beats Niou, who had been spending the match imitating Tezuka and Shiraishi. Fuji asks Tezuka right after if he can play a match with him. Tezuka accepts without hesitation. Very Touching.
What got this troper to continue watching The Prince of Tennis, after being so-so for some episodes, was having Sakuno and Ryoma meet up in the streets, Ryoma putting on his brand new regulars jacket to make her smile, Sakuno finally being able to congratulate him, and both kids walking home together as the sun sets.
And once Eiji wins his singles match against Kai? He immediately goes to Oishi, all smiles and telling him "you say how much I've grown, Oishi?" Whether you ship them or not, the "aaaaawwww" vibes kick in anyway.
Tezuka and Fuji's scenes as first graders. And the end of their anime-only duel. 'Nuff said.
The last minutes of the final OAV are one Crowning Moment of Heartwarming after another. Seeing Ryoma blush and smile happily as he and his teammates celebrate their final victory is priceless, and so is seeing Yukimura comforting a crying Kirihara, and then have Sanada giving him a towel and comforting him.
We can't forget Kawamura's return after being injured in the march with Kabaji, huh? And it's not exactly a return to tennis action, but him coming to cheer on Tezuka, who was this close to collapsing due to his injury. He does so by grabbing the Seigaku flag and waving it, despite his fomer injuries.
The first time we heard Kabaji say something aside of "Usu". He said "Thank you".
Double heartwarming when we see why he's saying that. It' because Atobe organized the whole Festival to cheer Kabaji up, after he falls into depression when his beloved older sister announces her marriage.
When Shiiba finally gets her Cool Big Sis ID with her adorable Kirk Summation towards a depressed Sakuno at the end of the Yamabuki arc.
The relationship between Fuji Shuusuke and his brother Yuuta starts out a Tear Jerker, but slowly becomes more of a CMOH as the series progresses. After Fuji wipes the floor with Mizuki for having no consideration for Yuuta's wellbeing, the latter slowly becomes less bitter towards the former, finally reaching the point of genuine admiration when he loudly proclaims that his older brother is "awesome" after Fuji develops his Final Counter in the match against Shiraishi.
Tezuka telling Ryoma that he'll always be Seigaku's Pillar of Support, no matter where he is. made even more heart-warming by the way they were smiling at each other