Im a huge Accelerator fan so i thought this was a fun little addition to the franchise! Just so you are aware this takes place during Accelerator and Last orders time in the hospital so youll wanna have at least watched season 1 of index or for a quick watch the sisters arc (episodes 10-14 of index or episodes 2-16 of Railgun S) and accelerator meeting last order (episodes 19 and 20 of index) if your a fan of the index and railgun series id definitely give thus one a watch!