Crowler and Jaden's season four duel. From wanting to get Jaden expelled in the beginning, three years earlier, Crowler now fights to keep him, and all of his friends in the school instead, not wanting them to leave him! It mirrors that first duel, right down to the monsters they played back then, and the entire school is cheering for them BOTH to win, even though if Crowler does, Jaden's whole class will be held back!
Crowler's duel against Chumley in season one also qualifies. If he could have let Chumley win, he would have, but it wouldn't have been fair like that. And he lets him go to his dream job anyway, because Chumley had proven that he earned it.
It was also one of the few times when Crowler was shown to be a professional. He dueled Chumley not solely to stop him from pursuing his dream, but rather as a teacher administering to a student a final exam to see if he/she was ready to venture out into the world. Despite the loss, Chumley proved to Dr. Crowler that he was able to make good decisions in both dueling and in life; and the duel itself was lost solely because Crowler had more experience than Chumley.
Also, for season four: when Jaden duels Nightshroud, and Nightshroud yanks Yubel out of Jaden's deck/soul and forces her to attack his monster. Due to Yubel's special effect, that would have caused Jaden to lose the duel. But he played a card so that she attacked him directly (Yubel has no attack points, so no damage was caused, thus her special effect was invalid). What's heartwarming is: he catches her fist, folds his hand over it gently, and tells her that he'll take her back, no matter what. *bawls just at the thought of it*
The scene in Season 1 ep 47 between Alexis and Zane qualifies in both languages. In the original, Asuka thanks Ryo for being an older brother to her while in the dub Zane jokingly offers to be her bodyguard and then tells her he'll miss her when he graduates.
Season 1, Episode 41: Alexis defeats Titan restoring her brother's memory. The ending of the episode (before The Reveal anyway) is one big D'awwww.
Another from Season 1: Zane's big bro moment with Syrus right before he throws the duel with Camula to save Sy's life.
Throughout season four, it seems that Jaden may never return to being his original happy persona. Thankfully, Winged Kuriboh induces some very convenient time travel, so that Jaden can face his idol: Yugi Moto, the King of Games. This duel rekindles Jaden's passion for dueling and returns him to his old, duel-loving self.
The last scene of the manga, in which Koyo has awakened from his coma, and is facing Judai in a duel as he promised
Also in the manga, in which, after Syrus loses to Chazz, Zane repeats his question of whether he wants to become a duelist. Rather than give his statement that he wants to "be" a pro duelist, which prompted Zane to doubt his resolve, Syrus says he wants to "fight as" a pro duelist, impressing Zane.
Jaden meeting Neo Spacian Aqua Dolphin, and at the end of the episode him telling Jaden he can count on the Neo Spacians as his allies and friends.
Crowler's duel against Bonaparte. Jaden boosts Crowler's confidence when he starts losing, he then tells Bonaparte that a good teacher is one that learns from his students