I Knew It: Early on, many fans hypothesized that Kaede would turn out to be a NEXT. Episode 17 proved them right.
Another very popular theory that turned out to be chillingly accurate come episode 19 was that Maverick was behind Barnaby's parents' deaths, and that he was the show's Big Bad.
Jossed: A popular theory about Barnaby being a robot was proven false. But this idea wasn't entirely a case of The Epileptic Trees, since androids were later introduced as something Maverick planned on using to replace Superheroes.
Mid Development Genre Shift: Of the first variety. Originally, the series was supposed to be much darker and more morbid in its theme and mood, with heavy drama and tragedy and different personalities for both main characters. The creators later decided to go for a more lighthearted story with an overall comedic theme accompanied by some drama; traces of the aforementioned serious tone can be seen in the second cour.
Playing Against Type: Most of Masakazu Morita's fans were surprised by the fact that he could go from being the seiyuu for hot-blooded shounen characters to voicing a character like Barnaby. Morita himself has expressed surprise that he was cast for the role, and says he sometimes felt that he might not be able to pull it off.
While her main role in the show, Agnes, is more the kind of character she's known for, Tara Platt also plays Samantha, a kindly old woman who was a nanny to Barnaby, who is voiced by her husband.
The Red Stapler: In Japan, products even tangentially related to the series are selling out — such as a brand of wine called Brooks that uses an Ouroboros on its label and a brand of cologne with a similarly shaped bottle to one Kotetsu owns.
Shrug of God: Regarding Kotetsu's actual age and the nature of Kotetsu and Barnaby's relationship.
Throw It In: When the producers told scriptwriter Masafumi Nishida that he could write the characters any way he wanted, he jokingly asked if one of them could be a photobombing weeaboo. The answer was yes.
What Could Have Been: The show was originally going to be called 'Busty and Bunny' (presumably, 'bust' meaning 'destroy'). Of course, then the female producer did some research and found out that they couldn't call him 'Busty', because of the English meaning. Another proposed title was 'Seekers'.
Kotetsu and Barnaby's powers were originally supposed to be memory manipulation and teleportation, respectively, making "Bunny" more of a Meaningful Name. But it was later decided that the two should be given similar abilities to highlight the differences in their personalities and attitudes. Each also wore the other's outfit, but they were swapped at the request of the director.
There was a ninth hero proposed early in development called Zen Beast, featuring a Split Personality. He was discarded because the creators wanted to have only eight heroes.