Iketeru Futari

Both are 6 minutes long with a total length of 16 epsiodes, Both focus on Comedy and Ecchi very heavily, In my opinion more so in Iketeru Futari, they also have an extra genre, In Colorful it's School, in Iketeru Futari it's Romance. Both have quite large casts, although the episodes in Colorful have segments, Iketeru Futari usually revolves around the 2 main characters. 

Akira Koizumi and Taiga Aisaka are characters cut from the same cloth. Both are short persons, live alone in a huge penthouse, have a rich yet broken family, resort to violent retribution and abrasive speech. Basically two S-tier tsunderes. The relation to both male MCs is a little less similar, but both stories fall into the range of high school romance with complex love polygon and rivals. While Toradora! oftentimes is pretty serious for a comedy and void of ecchi, Iketeru Futari in those aspect is the complete opposite. Both ecchi comedy tropes and scenes are up to eleven in it, and the plot doesn't even try to make real sense. However, they share the same humor and setting, so if you like one, you probably like the other. read more 

both mc are pervert 

Both have similar main heroes and the same humour. 

A stupid guy trying to get an awesome girl..both are funny and have like the same feeling.. 

Both involve crazy perverse men who are obsessed with one thing, but are really good and honest people. Plus both are hilarious 

the futari in the names! jk, both are really funny ecchi shows!