This is a 1993 OVA where WWII and alien invasion happen at the same time, and nobody stops fighting each other to deal with it. The premise is genuinely unsettling: humanity's worst impulse to destroy itself doesn't pause when existential threat shows up. Taishi gets thrown into giant robot warfare while the world refuses to unite, and the show treats this collision not as spectacle but as the actual hell it would be. It's a minor title that nobody remembers because it arrived in the wrong format at the wrong time. Watch it for the specific flavor of sci-fi dread that only works when you're trapped between two apocalypses at once.

October 1941: while humanity tears itself apart in global war, extraterrestrial forces descend on Earth with invasion on their minds. The Axis and Allies keep fighting each other even as this new threat emerges, leaving a unit called the Kishin Corps as the planet's only real defense. Its members field giant Geo-Armor Robots, known as Kishin, built from an alien robot soldier that was captured. Caught in the middle is Taishi, a teenager whose father, Professor Tokamura, has handed him a mysterious black attaché case. Inside is the control mechanism for one of the giant robots, and suddenly everyone is after it. The Japanese Kanto Army wants the device. The alien invaders want it. Even the Kishin Corps wants it back. Surrounded by spies, armies, aliens and towering machines, Taishi faces a sweeping mecha adventure, if he can live through it.