IS: Infinite Stratos 2 - Hitonatsu no Omoide

As the description says, it is extended footage of the first episode. It's mostly just a fan service episode so if you're into it, go for it. Otherwise you can skip it. There is absolutely no plot development here. Minor character development going on but it's mostly the girls fawning over Ichika again.

i wouldn't call this an extended version of the 1st episode of the 2nd season, But more like previously not shown footage, Maybe because they had to edited out after all they had to fit other things to an 12 Ep anime, I think they should have just made it to 13th episode, But it's not a bad episode, Fan Service for some charaters, Ichika as dense as ever and some shyness that some of you will find cute for some of the heroines, Anyways watch it, Don't lose anything by it.