I'd avoid any use of the word "otaku" to be honest. I know what it actually means and any person with some knowledge of Japanese culture would know what it means.
Unfortunately, in Western culture the word "otaku" carries negative connotations, implying fanaticism and unhealthy obsession.
I'd rather not waste any time explaining myself to people who don't know the true meaning of it and I'd rather not spend time defending myself and tolerating the inevitable slurs and condescension that will come with it.
I'd rather spend that time talking about SCANDAL and their music so I'm going to have to disagree with one the name suggestions.
Btw, I also think calling a SCANDAL fan Legionnaire only without any clue to the background of the fan group they belong to would be kind of confusing.
In order to work properly, a group of SCANDAL fans may be called SCANDAL Foreign Legion. SFL can be a name for a group of fans, not individuals.
DId that make sense at all? Haha..