Between 2013 and 2015, Studio 2.5 produced (somewhat fittingly) 25 cosplay videos, which were mostly parodies of popular media that made heavy use of special effects.
STAK-04, released in 2013, is a parody of A Certain Scientific Railgun and stars Anku Chacha as Shirai Kuroko and Sakura Sena as Misaka Mikoto (at least, I think that's right, though I can't say she much resembles the character she portrays).
Some short drama sections show the girls fight against a pair of masked adversaries with some not-particularly-impressive red beams.
There is a total of three sex scenes in this video: one featuring Chacha, one featuring Sena, and a girl-girl sex with both of them. Unfortunately they are nothing special (especially given they are filmed in very generic sets) and the mosaics are so massive that I wouldn't be surprised if the sex was entirely faked.
The main part of the video has a runtime of 1 hour 39 mins, which is followed by 35 mins of behind-the-scenes footage, which is only vaguely interesting and is mostly just clips of the sex scenes but filmed by an additional camera behind the main camera. Utterly pointless.
You might expect me to enjoy the drama sections and special effects of this video but, honestly, they are too brief and underwhelming to make them a reason to watch it. If Railgun-themed JAV is what you're looking for, you'd be much better off checking out HITMA-73. It has better costumes, better (and more) sex scenes, and is just all round a more polished product.
Score: 2.5/10