Sankaku no Sekai

Sankaku no Sekai is a silent science-fiction short film produced by the Shinshin Kinema company. The plot follows a grand, ominous convention held by the bizarre inhabitants of the "Triangular World," who gather to scheme the total annihilation of the human race. Meanwhile, the people of Earth must frantically devise a counter-strategy to defend their planet from the impending alien invasion.

(Source: Nihon Animation Eigashi, translated, edited)