IS: Infinite Stratos 2

Both series have the female character protagonists and antagonist completely dominant over society, Shidou(Main protagonist of Date A Live), is a lot like Ichika, accept the complete opposite at the same time. They deal with mecha, and action sequences similar to the animation of 8bit studios. This show won't disappoint you at all if you are looking for something to fill the void after Infinite Stratos. 

For me, the series has similar build to SAO itself from the first season. IS 2 has Houki and Tatenashi, SAO 2 has Asuna and Sinon. Of course Ichika is Kirito who is surrounded by girls developing a similar harem. The only difference is that the other genres are somewhat different. But both is set in the future. 

Above anime have lots in common with the fact that male protagonist is always surrounded by bunch of girls but is too dense to even understand and female's around him are too forward but also shy to directly tell him that !!! 

Harem anime with amazing art that have sibling yin-yang, meaning there are two girls in the harem that are sisters yet they have completely different personalities. 

Accel world is similar to Infinite Stratos 2 because of mecha type , but not fully mecha also ecchi and One Hero Basis . 

Both series features girls that represent different nations equipping combat machines created by a genius designed to help fight their enemies.  

Similar to their first seasons, both sequels feature a military school setting, pretty girls with special battle abilities, a dense male protagonist with a unique ability, plenty of sci-fi combat action and of course ecchi scenes. Differences include Freezing is more serious and is not really a harem where many girls love one guy (not yet anyway). Anyone who enjoyed Freezing or IS should definitely give the other a try, if you haven't already!