The concept of a school-based anime series without a sports day episode is preposterous; so it goes that this latest story arc of To Aru Majutsu no Index II begins with this franchises version of just such an event - a massive, Academy City wide sports day involving all of the schools within said city known as Daihaseisai.
Although this sounds like an excuse to throw in a filler episode, it isn't entirely filler-based - instead, we're drawn into a story of magicians entering Academy City thanks to the loosened security surrounding Daihaseisai and its many guests, with a view towards trading a sword known as "Stab Sword". Yes, it really does have a daft name like that, I didn't just pull that out of my ass no matter what you think.
That said, references to this deeper storyline are relatively isolated in this instalment (yet still too important to skip the episode, in case you're wondering), leaving us to spend much of the time enjoying Touma in various fan service-related shenanigans while he isn't getting second billing on-screen to Mikoto's tsundere behaviour or Index's insatiable hunger. Still, we do get to meet Misaka's mother briefly, if that helps thinks along at all.
At the risk of sounding prudish, I'm starting to get a little tired of the ramped up fan service in To Aru Majutsu no Index II - yes, it's titillating and sexy, but it's reaching the point of becoming distracting from the rest of the show, and I don't remember the franchise's first series going to anything like these lengths to grab its hardcore audience. That aside, this episode was okay - I can't otherwise fault it as a blend of fun but inconsequential filler than still has a sufficient eye towards a bigger picture, ready to mix the two elements up next time around. How this story arc as a whole will fare is still up in the air as a result, but I would wager a lot of it will depend on whether it can move its focus away from its various large-breasted characters to actually concentrate on the plot for a while.