The buildup to Yusuke's rematch with the Rhino Grongi is one for both him and his old school teacher Kanzaki. He lost all hope in his ability to teach kids and wondered if he couldn't give them the things they needed to succeed in life. And then, he learns that a promise he made with a certain man, to master 2000 skills before the year 2000 and to become a man who could protect the smiles of others, was made and honored. Thought his his thumbs-up was just another Character Tic of his? Well, now you know why he does it.
Kanzaki: Yusuke Godai! *Gives thumbs up* Do you know what this means? It came from Ancient Rome. It is a sign of affirmation. A gesture given to those who did what was right. You should aim to be someone worthy of that. Losing your father is indeed a sad thing, but because of that, for the sake of your mother and sister, you should become a man who can protect their smiles! Become a man who can protect everyone's smiles! Isn't that beautiful? Because Sensei... believes it is.
Note that Kanzaki basically summed up all of Yusuke's motivations and his character, nay, he GAVE him his character. If not for him, Yusuke wouldn't have become the All-Loving Hero that he is. Kanzaki essentially saved the world by cheering up a little kid.
Episode 33 has a scene between Yusuke and Detective Sugita, who only recently learned that Yusuke and Kuuga/Unidentified Life Form #4 are the same person. Sugita mentions that his daughter always felt #4 was a good guy. "Since #4 protected her daddy from #5, #4 has to be a good guy." The smile Yusuke gets afterwards shows how much it meant to hear that. Sugita then thanks Yusuke for saving his life that time, despite Yusuke protesting that there wasn't any need for thanks.
Followed up immediately by Sugita commenting about how, earlier in the series when they weren't sure if Kuuga wasn't another monster, he and several officers shot at him. Sugita clearly feels guilty about having done so and apologies, which Yusuke again tries to just brush off as unnecessary. When Sugita asks Yusuke why he kept helping them out, even after being treated like that, Yusuke simply says, "The same reason you guys are fighting." It's a very touching moment to establish how far Yusuke and the police have come together.
Practically the entirety of episode 47 and the first half of 48 involve Yusuke Godai meeting up with his friends to give himself strength for the Final Battle.
Episode 49, after all the horrifying damages caused by the Grongis, seeing the characters finally managing to return to their peaceful life, just bring a smile to you face. Especially the ending, with Yusuke traveling the world, no longer burdened with having to become Kuuga.
More meta than anything, but recent compiled information shows that the rumors that Joe Odagiri disliked his role as Godai aren't exactly based in reality. A particular heartwarmer is him attending the wedding of his onscreen sister!