I'd been wondering about that, too, after getting a Game Jobs e-mail alert about their new job posting (though I didn't end up applying), so I just went to google and ran the same sort of searches that I usually do for things like that, and it looks pretty legitimate. For writing jobs, I've found out about plenty of scams that way, and if Mashiyu Entertainment is a bit dicey, they're a lot smarter about hiding it than other things I've done research on. It looks like they're a fairly proper company, but I just searched for it in association with job scams, stories from anonymous employees, and Better Business Bureau reports, so I'm sure there's more that could be done if you're still concerned. There wasn't really enough information about it on any front to be sure about their intentions at all.
(It's a bit of a "well, I guess I don't really know at all!" answer, but I hope it can still be helpful.)