Items not shown in the library through home sharing on other accounts.

All content is tied to the account that downloaded it, you won't see an account's purchases on a different account.

You could copy them back from your backup of your downloads/library and add them to your iTunes library via File > Add To Library. Or when you are back in Hong Kong (you have to be in a country to use its store, including redownloading past purchases, otherwise you would be violating the store's terms and Apple could permanently disable the account), and if the songs are still in the store at the time, you might be able to redownload them.

I can download both Hong Kong and Japan App Store contents which different account.

Not entirely sure what that means An account's past purchases can only potentially be redownloaded by the account(s) that originally bought/downloaded it from the store. If the rights-holder has removed an item from the store (songs, albums, apps etc could be removed at any time) then they won't show for redownloading (they also won't show in the Purchased tab if you've hidden them from the cloud : Hide and unhide purchases in iTunes or iBooks on your Mac or PC - Apple Support)

Are you in the relevant country when using its store (including redownloading) i.e. only using the Hong Kong when physically within Hong Kong (and similarly for the Japan account) ? If not the Apple might permanently disable the account