Thread:LordRimus/@comment-31179625-20170130001650

That isn't sieghart check your sources please, it's a character from Netoge Haiakuma no Negai Kanaemasu(ネトゲ廃悪魔の願い叶えます).

See this thread on reddit for confirmation!

Baka-tsuki added it but ISN'T an official illustration for Mushoku Tensei INSTEAD an official illustration for Netoge Haiakuma no Negai Kanaemasu. 