Dororo is a main character from Sgt. Frog/Keroro Gunsou anime & manga series.
He is a blue sadsack ninja boy. He even cosplays as Ariel from Disney's The Little Mermaid movie.
While Dororo is never officially shown without his mask in the original anime & manga series, There are several attempts to resolve this age-old issue of seeing him without his mask, like "Dororo without his mask" drawn by Aoihitodayo from Instagram Japan.