Episode 57: Pages 133-147 of volume 4 of the Kodansha publication.
Very fast paced chapter! Gotta love the moments where we can just watch Chiyoko waste a whole room of dudes with her brute strength. Although, the boys' excited reaction to Kei being a woman tells me that Tetsuo's little "hobby" might've dwindled the female population down quite a bit in the Great Tokyo Empire.