Kemuzou Kemumaki

Kemuzou Kemumaki is a Koga Ninja and the main antagonist of Ninja Hattori-kun. He lives in a block of flats with his cat Kagechiyo, and happens to be the opposite of Kenichi Mitsuba. He loves Yumeko, but the reason why he dislikes Kenichi is because he loves her too. However, he is scared of some of Hattori's ninja techniques, and can easily be intimidated by him. Kemumaki comes from the Koga clan, and the Ega and Koga clan are sworn rivals. Hence Kemumaki hates Hattori and challenges him often.

(Source: Ninja Hattori-kun Wiki)