Seri Tatekami serves as a student and second-generation Fafner pilot on Tatsumiyajima Island, operating the Mark Zwolf unit. She possesses grey eyes and black hair, which turns white during the events of Soukyuu no Fafner The Beyond. A member of the biology club, Seri is among the first to befriend Tsubaki Minashiro following Tsubaki's emergence from isolation. Their friendship begins when Seri encounters Tsubaki while hiding during the island's initial invasion; Seri shares details of her daily life and club activities, offering reassurance when Tsubaki departs in a transport tube.

As Tatsumiyajima's conflict intensifies, Seri transitions into active combat, participating in simulations and real engagements during Soukyuu no Fafner Exodus. She launches in her first battle using the Levin Sword and Shotgun Horn against Festum, undergoing medical examinations after combat. Seri maintains her connection with Tsubaki, visiting her core in the Exodus timeline and expressing concern over creating additional cores, believing Tsubaki wouldn't wish combat on others. She later distributes protective charms to new third-generation pilots, acknowledging past tragedies like the Plan L incident.

During Soukyuu no Fafner The Beyond, Seri participates in the Sixth Operation Azure, destroying Leviathan-type Festum around the L-Boat and aiding in the defense against the Mark Raison alongside allies such as Abaddon. Surviving the operation, she returns to Tatsumiyajima, reuniting with friends like Rina Nishio. In the aftermath, she guides Sakura Kondou to her mother's resting place and attends memorial sites for fallen characters. She also observes key figures departing the island during the Tanabata Festival. Her background includes family connections, referenced when discussing receiving a charm with her father and guiding Sakura to her mother's resting place.