Akibaranger is, to put it simply, a parody. It stars these three guys:
who, using the figures they're holding, become these guys:
and yes, it never goes beyond those three. It's a reference to these guys:
http://img2.wikia.nocookie.net/__cb20110130081216/powerrangers/images/f/fc/B0096882_20293954.jpg
Sun Vulcan. Though, the red, Nobuo Akagi, thinks they're gonna get two more, like Hurikenger. It takes place in a world pretty much like ours, including Super Sentai just being a TV Show. It's pretty great, clocking in at 13 episodes as opposed to Sentai's more traditional 48-50, though it did get a second season. While it parodies existing sentai patterns and themes, it's still unashamedly doing the same thing, producing a predictable yet cool twist and genuinely fun action sequences, including one of the best Final Boss fights of any sentai ever.