DT #633 Parallelism

The recent movie "300: Rise of an Empire" has been described as a X to the film "300". This is primarily because the events in both the movies run mostly parallel to each other. Thus, it cannot be described as either a sequel or a prequel.

Some even term the 2012 movie "The Bourne Legacy" as a X to the previous movie "The Bourne Ultimatum" because parts of the former take place at the same time as the latter.

Identify X.