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Simply contrasting cities within the setting is Athens and Sparta, but after reading your example I'm not so sure this is really what you mean. Elaborate maybe?
@Veanne
Tetsunagi Island has the hallmarks of a city that is within the 20th or 21st century, heck even 19th century, while every other city outside of the island is a staple futuristic city in the distant future. Plus there is no grim/harsh nature as you mentioned about Athens and Sparta since the whole manga is an Iyashikei.
The Futuristic City seen in Ch. 10
Alright then, let's see if I understand you. This is a futuristic world with an enclave of 20th/21th century. The enclave isn't caused by any sort of segregation (what is it caused by? is it a tourist town?) and the general tone of the story tends towards the heartwarming and fluffy.
If this is correct then, in trope-speak, we have a Crystal Spires and Togas in a Decade Dissonance with a... well, I was thinking a Hidden Elf Village, but it's not hidden, is it? It doesn't seem to be Arcadia either. I thought Juxtaposition Tropes would have something, but Decade Dissonance seems the only trope there that fits.
Tetsunagi Island is like a tourist town where sentient animals (emphasis for sentient) and humans intermingle with each other, but it's, as you said, like an enclave of a 20th/21st century world, whereas everywhere else outside of it is very futuristic.
I guess that's a much clearer explanation.
Edited by holygrail24 The Metro series fan! Steam Account: Randum
Decade Dissonance sounds closest, then. Maybe even Exagerrated.
There's Culturally Distinct Neighborhood which draws from the Amish example in RL.
What is the trope where there is a futuristic city while the primary setting the protagonists have is a reminiscent of a city from either 20th or 21st Century? Rich/poor division is not the focus here, so it will not be Urban Segregation.
Context from Twilight Star Sui and Neri: