Artist.
Japanese name: ぱくちー (Pakuchii)
The other names: せんじゅ (Senju), 千寿ぱくちー (Senju Pakuchii) or gpeas
Circle name: おいしいアメジスト (Oishii Amethyst) (circle partgiven name: Kotetsu Etsuo)
Old joint circle name: 兎想幻酒帳 (Tosou Genshuchou)
(The artist had a tegaki blog account, too.)