Has there been any episode of Go-Busters that's been like completely filler?I mean even the filler episodes kinda progressed the plot in some kind of way, be it BC-04,debuting something, or learning some back story....
Well, let's see...
Episode 1: Introduced the team, the setting, Enter
Episode 2: Reveals a bit more of the team's backstory, primarily Hiromu's promise to Yoko
Episode 3: Mostly filler, but of note is that Yoko and Hiromu come to an understanding and stop fighting (mostly)
Episode 4: More info on the Metaloid/Megazord connection, as well as stuff regarding Kuroki's determination.
Episode 5: Introduction of Ryuuji's "dark side"
Episode 6: Introduction of Go-Buster Oh
Episode 7: Mostly filler, some character development for Hiromu
Episode 8: Introduction of the blueprints for the 4th Buster Machine
Episode 9: Mostly filler, some development for Yoko and Usada
Episode 10: More developments regarding BC-04, Rika accepts Nick
Episode 11: Mostly filler, some development for Gorisaki and Ryuuji
Episode 12: Mostly filler, some development for Yoko
Episode 13: Mostly filler, development for Yoko, first true 2-parter (part 1)
Episode 14: First true 2-parter (part 2), development for Yoko, first appearance of Jin and J (cameo at the end)
Episode 15: [proper] Introduction of Jin and J
Episode 16: Story on Jin and the other researchers, including heavy hints that Hiromu and Yoko's parents are still alive, and a bit on the nature of Avatars
Episode 17: First appearance of Go-Buster Beet
Episode 18: Mostly filler, introduces Jin ordering J to follow/protect Yoko
Episode 19: Introduction of Buster Hercules, some development for Nick
Episode 20: Introduction of Great Go-Buster, introduction of the subspace projection field
Episode 21: Mostly filler,
slight development for Ryuuji (not much)
Episode 22: Introduction of Escape
Episode 23: Backstory on Jin and Yoko's mother, introduction of the GB-Protection suit
Episode 24: Mostly filler, some development for Hiromu
Episode 25: Mostly filler, some development for Ryuuji, more info on those trapped in subspace
Episode 26: Mostly filler, some development for Nakamura
Episode 27: Enter tries to get Dr Kudo to evolve Messiah
Episode 28: [Note that I haven't seen this subbed yet] Stuff is going on with Messiah, due to last episode, and there seems to be a connection between Escape and Hiromu's mom. Also, something's going on with Jin
Of those, even with the character development, I'd consider most of the "mostly filler" ones (7, 9, 11, 12, 21, 24, 25, and 26) close enough to be full filler episodes, especially 21 and 26. However, if you count character development as non-filler, then no, there haven't been any pure filler episodes, IMO.