Thunder Spirits is a 1991 SNES port of the arcade title Thunder Force AC, which itself was a modified port of the highly-praised Sega Genesis title Thunder Force III developed by Technosoft. The port was published by Seika Corporation.
When compared with the Genesis title, gameplay-wise they were nearly identical, with the only real differences being the Heads Up Display being moved from the top to the bottom of the screen, minor alterations to some of the levels, and the removal of the ability to choose the order in which the player completed the levels. However, it suffered from the notorious "slowdown" that plagued many early Super Nintendo titles when too much activity on the screen at once would overtax the system. A loss in music and sound effects quality was present as well.