More info about this doujin is available at:

http://shink.me/mSbDA

artist: SHIYAMI
artist: Yasamata Shiyami

Masaya Miyashita is the real name of the artist using the pseudonym "SHIYAMI" or "Yasamata Shiyami" in the database. A number of years ago, this artist had been arrested for publishing doujinshi. I don't know if the regulatory troubles had resulted in the artist using multiple pseudonyms or different ones since 2008. An overview of what happened is at:
http://www.rqq.co/BhvVo

The circle "S-Plus" is the most stable reference for this artist. The artist used various names such as "SHIYAMI" or "Yasamata Shiyami" for doujin and PC HCG works while maintaining his professional artist name as Masaya Miyashita.

See the artist's archived homepages for proof of the various names he used:
http://www.rqq.co/BhvWu
http://linkshrink.net/7k8yWF

So, do all the different works by the artist as "shiyami" and "yasamata shiyami" get aggregated under the artist's real name of "Masaya Miyashita"?

Base +21