Formerly inactive artist, who posted this image on November 5, 2019 before deleting their twitter account shortly thereafter.
Some detailed speculation regarding the deletion can be found here (written in Chinese)
Came back in November.

Nickname: スメタナ (Smetana / Sumetana)

See also

• Pawoo account: https://pawoo.net/@HamsterFragment
• Pixiv account (deleted): https://www.pixiv.net/member.php?id=17494898
• Twitter account: https://twitter.com/HamsterFragment