Actually officially you do need permission and are not allowed to do it. In their FAQ they say this:
[quote:2tjuu38n]But you're allowed to do that?...
...no. We could be if this was a parody (like the well-known Spanish Dragon Fall), but here, we'd need the copyright, and we will never get it.
But, as we don't sell this comic, there is no reason to stop us from giving publicity to Dragon Ball
In japan, fan-comics like this one, named Dôjinshi, are very popular and numerous.
Which means whoever owns the copyright can stop you at anytime. I am just making sure you are aware so IF it happens it isn't a complete surprise that you have to remove everything you worked hard to produce.