Afraid you are going to be told to get a real computer or dual boot (parallels if you are unfamiliar with the concept) or run a VM (on Windows I quite like virtualbox but the mac set seem to plump for vmware's offerings), or hope wine/cider is up to the task (not impossible but I would not bank on it). I am not aware of any java options either if you were thinking about coming that way. ROM hacking has historically been and probably will remain a Windows only affair for the foreseeable future if you don't want to hand make your own tools. I am sort of surprised that nobody has made a quick and dirty port of a few tools but at the same time there are so few mac users and osx confers no benefit to ROM hacking so hey.
You might find a hex editor with basic shiftJIS support, though probably not really any good for ROM hacking (so many DS games use 16 bit encodings like shiftJIS but can end with 8 bit control characters meaning every other line or worse is not aligned and that breaks most text/basic hex editor decoding options).