Shinseiki Evangelion (新世紀エヴァンゲリオン), sometimes colloquially referred to as "Shinseiki Evangelion: 1st Impression", is a video game released exclusively for the Japanese Sega Saturn on March 1st 1996. It is the first video game based on the Evangelion anime series. It features a new original Angel, the Unnamed Angel. It was initially marketed as "Episode X" in the advertising before its release.
This is an FMV game that features both original and repurposed animation from the TV series. The story is said to take place between the 8th and 9th episodes of the anime. The player's choices actually influence the flow of the story and can lead to three very different endings. Upon completing the game the first time, a "Replay" mode is unlocked which allows you to watch the events of the game as if it were an episode of the series, complete with the show's opening and ending credits.
A newer edition of the game featuring the "1st Impression" subtitle was released on February 4th 1997, just one month prior to the follow-up title's release.
Source: Evangelion.Fandom, "Shinseiki Evangelion (Sega Saturn)", available under the CC-BY-SA License.