Believing all biological life must be purged, Ultron and Sigma forge an alliance. Using the Reality and Space Infinity Stones, they fuse themselves into a single being named "Ultron Sigma", and merge the worlds of Marvel and Capcom into a single dimension, which they seek to rule by unleashing a cybernetic virus that puts others under their control. As a result, the heroes of both worlds must band together to retrieve the remaining four Infinity Stones with the now-captured Thanos' help, and defeat both Ultron Sigma's forces and a deadly group of villains led by Jedah Dohma, who wish to unleash terror on the merged world using the power of the Symbiotes.