|This article is about a/an episode in Himitsu Sentai Gorenger.|
The Big Blue Fortress! Big Raging Variblune (青い大要塞! 大暴れバリブルーン Aoi Dai Yōsai! Dai Abareru Bariburūn?) is the fifteenth episode of Himitsu Sentai Gorenger. It introduces Sun Halo Mask. It is also the first episode with Tōru Ōhira as narrator, taking over from Nobuo Tanaka. It received a theatrical showing as Himitsu Sentai Gorenger: The Blue Fortress.
A mission to take down a Black Cross fortress becomes hampered when a Masked Monster, under the direction of a returned general, takes Variblune from Shinmei for their usage.
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- This episode aired on NET the same day episode 17 of Kamen Rider Stronger, Ghost Story, The Demonic Easter, aired on TBS.
Himitsu Sentai Gorenger Volume 3 features episodes 13-18: Ep. 13: The Pink Secret! Defeat the Human Bomb, Ep. 14: The Red Coffin! The Mysterious Skull Mansion, Ep. 15: The Big Blue Fortress! Big Raging Variblune, Ep. 16: White Weirdness! The Eye in the Mirror, Ep. 17: The Purple Theme Park! A Demonic Cemetery, and Ep. 18: Horrible Black Crusaders! Attack According to the (Secret) Plan. 
Blu-ray Box 1 comes with 16 episodes.