Artist. Formerly tagged as yuuichi_(pixiv415516).
Japanese name: ゆういち (Yuuichi)
Circle & site name: 下野会 (Shimotsuke-kai)
https://www.pixiv.net/users/415516
https://www.pixiv.net/stacc/sk_you_1
https://c10016279.circle.ms/oc/CircleProfile.aspx/
https://c10049277.circle.ms/oc/CircleProfile.aspx/
http://www.melonbooks.com/index.php?main_page=maker_info&makers_id=MK0000003887