Artist. Possibly another artist's second accounts.

Japanese name: 屋 (correct reading is unknown)
The other names: ユケ (Yuke), ユケオ (Yukeo), うこ (Uko), "(●◎○)" or 信号機 (Shingouki)

See also

• Twitter account: http://twitter.com/yukeosan
• Privatter account: http://privatter.net/u/yukeosan
• Old twitter (deleted): http://twitter.com/ukow0
• Old privatter: http://privatter.net/u/ukow0

(The artist had a Flipnote Hatena account, too.)