Chrono Trigger scribe Masato Kato was credited for "ART WORKS" in the original Ninja Gaiden. From a recent interview:

Basically, I was responsible for the backgrounds, the hero and enemies for the action part. Beyond that, I did also images for the Cinema Display. Those were all pixel graphics. Furthermore, I drew the images for the enemy introductions in the manual. Since my drawings hold some peculiarities, I think people who know (my style) might recognize it there.

See The Chrono Trigger - Ninja Gaiden Connection for more about Kato's work on the Ninja Gaiden series and some interesting insight into the peculiarities of Japanese pseudonyms in the NES era.