Following the success of field testing the Jetta unit, the JSDF looked into creating an infiltration mecha that could mingle with the k-girls in their own habitats, passing off as one of them before striking at the intended target with maximum force.

Katsura, the mecha k-girl based off of the sadistic machine created by the Simeons to lead their invasion of planet Earth, was built some time during the mid-2010’s to fulfill this designation. Not only based on the alien mecha, but employing technology salvaged from the mangled remains left behind after the machine's battle with Godzilla in 1975 as well as having a partly human AI thanks to cybernetic tech removed from the brain of a Simeon infiltrator (who is also Katsura's namesake), Katsura was the first in the Mecha-Gina line of robots, followed by Sumegi and Kiryuu.

Her first objective, after extensive testing of her abilities (such as passing by the k-girl living areas in the designated disguise, greeting the various anthromorphic beings from afar and observing the response) was to infiltrate the institution known as Daikaiju High while equipped with the GINA-class disguise, and garner as much information as possible about the various attendees. Katsura, having been built with all hitherto gathered information on Gina (thanks to various files reluctantly given to the JSDF by the Daikaiju High staff, and extensive observation of the k-girl by elite army units) was able to fully integrate herself into the community (Gina herself being away from class due to a rare cold), and during this integration she got to spend quite some time with the k-girl known as Titanna (this close proximity to the cheerful-yet-modest Titanna seems to have had some form of impact on Katsura’s partly human AI, as the mecha girl has been seen together with the k-girl several times even after her infiltration mission was compromised).

However, just as Katsura was about to commence the second stage of her mission (the JSDF have been reluctant to hand out any information as to what this ‘second stage’ was) she was viscously attacked by Angi-lass, who tore of her disguise to reveal the metallic exoskeleton underneath (Angi, having spent the day caring for Gina before heading off to school several hours after the other girls, was not fooled by the mecha’s suit). The following battle left Angi badly mauled by the far superior Katsura, who was herself smashed when Gina got news of the ongoing (one-sided) struggle between the two girls.

Today, Katsura (upgraded with a new personality and additional equipment) is a part-time attendee, full-time security officer at DKH alongside her ‘sisters’ Sumegi and Kiryuu (both commissioned after the construction of Katsura as a means of forming new attack strategies), and while her rivalry with Gina and Angi has not cooled visibly, she has found a surprising friend in Titanna, who still sees a part of the Gina-influenced personality within the mecha girl.