Metal Storm was released on April 24, 1992 in Japan. One year after the USA release (1991) but this Japanese released should be considered as the original since the game was developed in Japan.
[US] "Metal Storm [Model NES-4M-USA]
Although the Famicom does not directly support parallax scrolling, programmers continuously redrew the tiles making up the game's backgrounds in order to animate them scrolling at a different rate than the foreground, giving an illusion of depth, notably in the game's third and fifth stages where there is a second background layer that appears to scroll behind the first.
Cameo: During stage 6 boss fight, the battleship from stage 3 of the first R-Type can be seen several times in the background.