The first thing is first, 2013?! what a great anime to have aged so damn well. Secondly, the sisters are just the best as usual with the way they speak especially.
The story is a continuation of the main story and can be slotted into the index series at various points if you want proper order. I watched it after watching all of the index shows and it still works.
The art as I said has aged very well and is a super thing to watch considering its age.
The OP and ED are fun and the sound is great for it's age. The voices of course with Shirai and the sisters are phenomenal.
The characters you can still care about and you really understand many situations and have some introduced early for what can only be expected as a later upcoming thing.
I especially enjoyed Saten as usual but also Frenda and Shinobu too. You will see why.
From start to finish you have great scenes and storytelling. You get some pretty odd situations that get a bit out of line with the story like sudden mechas showing up that wasn't needed and the finale was a bit rushed with not so much involvement from some characters as I'd of liked to see.
8/10.
