{ key => 'k', class => 'kanji' },
[download]

is best here because it makes it easy to see the differences the rows at a glance.

    {
        key => 'k', class => 'kanji'
    },
[download]

isn't too bad, since it's almost as good at showing the differences between rows. The extra spacing is a needless hindrance, though, so it's not as good.

But it's definitely not as bad as what you posted in the OP.

    {
        key => 'k', class => 'kanji' },
[download]

This is just plain weird.

Finally, we have this:

   {
      key => 'k',
      class => 'kanji',
   },
[download]

It offers no readability benefits over the styles, and makes it even harder to see differences between the lines. No good here. This would be used when dealing with with very long records, and when adjacent lines are substantially different (e.g. in a multi-level structure).