As far as I understand, it's one of those games where you launch a ball and clear as many blocks as possible, in order to show the background image. Like this one:
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Except that the game is quite old and it is not based on Javascript, but on Java (html\BakuBlockV77.class is an applet, I guess).
More than a decade ago, web pages used to embed small Java programs. Browsers nowadays don't support Java anymore though.
If you reaaaaaaaaaaaaaaaally want to play the game, I guess you can:
1. find a version that uses Javascript
2. convert the applet into Javascript (JSweet? CheerpJ?)
3. try one of the solutions discussed
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4. set up a virtual machine with Windows 2000, install Java and launch the game with IE (kek)
5. ???
Or you can just be satisfied with the gallery mode.