>>32373
It's from a bad Japanese wordplay pun (which they love).
The Combloc girls go to "Akagane-kou," or Red Steel School (aka = red, gane = steel/metal, kou = school).
If you break up Akagane-kou into it's constituent syllables, it vaguely becomes "AKs are cats."
>Akagane-kou
>AK ga neko
>AK are/is cat
>AKs are cats