Ekaterina II S (エカテリーナ二世号・改 Ekaterīna Nisei-gō Kai?) is a large general purpose transforming robot manufactured by Kongou Airlines in Academy City. It is named after Kongou Mitsuko's pet python Ekaterina.
Initially looking like a large utility truck, it can transform into a large Powered Suit, similar to that of Multi Active Rescue's Gigantic Advanced Movement Armor. Like it, it has wheels upon its feet to roll on a flat surface and has been shown to be very quick. It also has clamps for grabbing things, as well as a pile bunker. It's arms and legs can be disconnected from the torso.
It requires two people to pilot it, and is apparently easy enough for two middle-schoolers, like Uiharu Kazari and Saten Ruiko, to pilot it during combat without experience and only a single night of studying its manual. Thanks to Ekaterina II, they were able to defeat the two mobile weapons owned by STUDY, during the Silent Party.