Episode 77: Pages 84-102 of volume 5 of the Kodansha publication.
Seeing Kaneda and Kai ride through the empty subways looks so cool honestly. I always love looking at the attention to detail in the architecture and backgrounds Otomo draws.
The chapter ends with Kei finding Chiyoko still alive but weak, the Great Tokyo Empire about to break in, and Kaneda and Kai finding a Kei ghost in the subway tunnel.