Some time in early 1998 I picked up this laminated bootleg poster from Japan Video in San Francisco's Japantown. At the time I found the image quite striking, especially Asuka's tears and Rei leaning against an open entry plug. Eva-01 is derived from the scene after it consumes Zeruel. However I had not been been able to identify the entire image as I had never seen it before despite my extensive browsing of Eva imagery at the time on the web, back when I was building my Asuka picture shrine.
Recently I was checking out Surugaya-a-too's storefront and came across the doujin anthology Traitorous Angel. Using Google Images to check it out turns up this very illustration, which actually appears in Traitorous Angel 2. I guess whoever designed the poster felt that a white background wasn't enough. Mystery solved after 15 years.
Update: Thanks to my collecting buddy DrScorpio, the artist has been identified as Koh Kawarajima, a member of the doujin circle Henrenkai. Kawarajima is a duo, Kazuaki Kawashima and Hiroyuki Karashima. I actually have their Traumerei art book in which this illustration appears, but since I had gotten that a couple years before the poster, just hadn't made the connection.