So we Tsukasa in her normal age watching the Eiffel Tower being built in 1887, but watching her walking through what we assume a bombed out city, could be during WWII 1945, she looks younger. It's a weird timeskip because we know she's been to Paris before but surely not at such a young age.
My second guess is in the cover she's watching the Tokyo tower being built which was in 1957.
I'm not sure if this will be explained later on in future chapters, I've only read up to this point now.