Another idea that I may not use. I just came up with it.

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Across the Universe (Voltron x Ultraman Nexus Crossover)

After Shiro's disappearance, the paladins scramble to form Voltron and hold off against the Galra Empire. However, the void left behind by Shiro is hard to fill, causing Pidge to create a machine to find him....

Meanwhile, in a battle against a beast, Himeya is forced out of his Ultraman form and sucked into a portal with Komon, where they meet Takashi Shirogane and Matt Holt - two men who have lost their memories. Banding together, they must find their way back before the shadow of Lotor engulfs them....

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If I were to do this it'll have Keith x Lance and Himeya x Komon. And Shiro x Allura.