.mbb is not a known format as far as I know. This means you will likely end up having to manually work with the files, or building a tool to handle it. Plenty of new hackers have done both of those over the years so don't get disheartened.
Decoded files like that are not of the most use -- I might be able to spot some patterns and work backwards but at the same time such things will lose data if it can't decode it (same thing why you can't open up a binary file in notepad, do nothing to it, press save and expect it to work afterwards) so that is not a great thing. Raw hex is usually a better bet for someone around here to make some quick calls without having to fetch the ROM to look at themselves.
That said what is in the other files there with _DE _EN _ES.. in the name*?
http://www.advanscene.com/ says it is just multi5 so I have to wonder if that is not something else -- 5 languages and an index file of sorts. It could still be a Japanese script that they blocked (happens from time to time, we are told it is mostly to stop people importing the games from outside Japan for cheaper).
*DE= Deutsch = German, EN = English, ES = español = Spanish, FR = Francais = French, IT = Italiano = I have no idea actually, just one of those mysteries in the world.