I seriously like the interaction Gohan and Piccolo had during the end of the movie.
Piccolo having no idea that Gohan was going to use the SBC and yet sees him pull off probably the best one in the series had to have made Piccolo feel so special.
Piccolo’s first student and best friend, whom he thought pretty much gave up on martial arts, practiced his sensei’s most iconic movie in secret and used it masterfully to end the biggest threat Earth had faced up to date.
When asked about it, Gohan simply said that it was supposed to be a SBC, and he’s been practicing it in secret. Piccolo trying to conceal his emotion tells him it was great. But it’s clear he had more to say.
During the whole fight Piccolo had the utmost faith in Gohan, and was willing to sacrifice his life to give an opportunity at a finishing blow. Piccolo even expected it to be a Kamehameha, I can only imagine the emotion he felt when his effort was rewarded with seeing his own technique.
Gohan using this move means that he had not completely given up martial arts like all the full time warriors had believed, and found time to practice a move from the Demon Clan style in the midst of being a full time father, husband, and professor. Piccolo was not expecting this at all seeing as he watches Pan and is aware that Gohan doesn’t train due to sizing him up regularly.
You can feel the disappointment in Piccolo throughout the movie seeing his pride and joy not being able to sense him and looking like a shell of the former warrior he was. I like that Piccolo didn’t give up on Gohan and made attempts to bring him back to all his glory. He got paid back in full with compound interest. Piccolo would’ve taken a Kamehameha from his favorite student, but got a SBC instead.