Episodes 7-9 of the Soukyuu no Fafner: Dead Aggressor - The Beyond series.

After a school trip goes terribly wrong, Homare Onishima, Shion Kujou, Asuka Suzumori, and Mutsu Amatani are left stranded on a deserted island. While Shion, Asuka, and Mutsu are frightened and desperate, Homare seems strangely calm. Fortunately for the group, this isn't the first time she's been stranded! Homare spent her childhood training with her survivalist father all over the world, climbing cliffs, trapping prey, building shelters, and obtaining valuable nutrition from moose testicles. To Homare, surviving on an uninhabited island with a slim chance of rescue is child's play. The only problem is the other three. As Homare shamelessly guides her classmates through the finer points of survival, including drinking fish blood and eating cicadas, the girls start to realize that being stranded might not be as bad as they had imagined.

Episodes 4-6 of the Soukyuu no Fafner: Dead Aggressor - The Beyond series.

Tatsumiyajima is the central island in the middle of a small cluster of islands, in a sleepy backwater of the Japanese isles. Not much happens there, and the island's young people go to school knowing that their lives are likely to remain peaceful and undisturbed. Or so they have been taught... but the truth is different. The fate of mankind is on the line, and Tatsumiyajima is the last line of defense against a hostile and incomprehensible enemy. At the center of it all, fighting for Humanity's continued existence, is the giant robot Fafner, the dragon that guards this final treasure of mankind. (Source: ANN)