The top cases are the same except the key layout as the Japanese one is ISO and the US is setup for North America which alters the Right Shift and Return keys.
Its a bit of works you’ll need to strip the battery if the case doesn’t offer one (recommend getting it with battery) Do make sure you are very careful removing the TouchID button [guide|142681] as you’ll need to transfer that over with the logic board.
13” MacBook Air Top Case & US Keyboard:
* Space Grey Apple P/N 661-15386
* Silver Apple P/N 661-15387
* Gold Apple P/N 661-15388
Be aware these are around $360 USD without the battery which is another $130. Given the cost and the work needed is it worth the effort? Maybe getting a good thin keyboard skin would be better with the proper markings. Or, look at buying another with the proper keyboard and after you’ve transferred things sell yours. You might even find a Japanese version if you really want that keyboard layout. If you only have a few broken keycaps see if you can get the needed replacements here: [https://www.thebookyard.com/apple-keycaps.php?cPath=66_504_813_734|2020 MacBook Air KeyCaps]