I believe theNow solved in full after helpful pointers in comments from @GarethMcCaughan and @Deusovi - my thanks to both!
The completed crossword should look something like this:
AsIn fact, we need to go a little further, and also apply this to the four single letters indicated in grey...
...since these individual vowels also have their own Japanese characters:
We now need to take note of the poem at the top of the puzzle, because this is giving us a very important clue (thanks to @Deusovi in comments for this part)...
It turns out that there is a very famous Japanese poem called Iroha, which famously is a pangram that uses all 47 characters of the Japanese syllabary exactly once (NB with the exception of ん (-n), which was not distinguished from む (mu) in writing until the early 20th century (Source: Wikipedia)):
以呂波耳本部止
千利奴流乎和加
餘多連曽津祢那
良牟有為能於久
耶万計不己衣天
阿佐伎喩女美之
恵比毛勢須
And this should point us towards the fact (noted by @GarethMcCaughan in comments) that each of the characters used in the crossword grid appears just once. In fact, we have used 40 of the 47 characters and only seven remain unused. If we strike off all those that have been utilised up to this point, we are now left with:
KA, KI, I, TSU, SU, YO and TO
Finally, for the landmark represented in the crossword, I believewe can now see that this is likely to be:
Tōkyō Sukaitsurī (a.k.a. 'Tokyo Skytree') - a neo-futurist building (hence the title) in the Japanese capital:
This does endends in the 'RI' present in the grid in answer 2A. However, I must confess I am at somewhat of a loss asand we are able to whatarrange the numbers are intendedseven unused syllables into these boxes to represent herespell out its name, or why there are four grey boxesending in the crossword grid indicating'RI':
TO-KI-YO SU-KA-I-TSU-RI
The numbers specifically refer to the vowels Uorder in which they appear in the pangram: 2 TO, O6 KI, A4 YO, and E..7 SU, 3 KA, 1 I, 5 TSU.