A missing artist.
Japanese name: 妹撃 すたん (spelling used by the artist: "Imouchi Stan" / danbooru's official romanization: "Imouchi Sutan")
The other name: すたん (Stan or Sutan)
Site name: マッシュルーム樹海 or すたんさんのハウス
It seems to be an old account of the artist below.
Nickname: 今日も役立たず (Kyou mo Yakutatazu)
The other names: 妹撃 州丹, 妹撃 すたん (reading is given as いもうちすたん, Imouchi Sutan or Imouchi Stan) or "stan_imouchi"
Site names: 州丹庵 or 新装！州丹庵