Kenichi Mitsuba (三葉ケン一 Mitsuba Kenichi) is the deuteragonist of the Ninja Hattori-kun franchise. He is an eleven-year-old boy who goes to the local comprehensive school. His parents are Kentaru Mitsuba and Mrs Mitsuba. He often gets low marks in his exams. He is in love with Yumeko Kawai, however, his arch-rival Kemuzou Kemumaki is always after her.
Kenichi is slim, round faced, has small black eyes, pale skin and black hair with three fringes at the forehead. He often wears a sky-blue long-sleeved T-shirt with red-and-yellow stripes, dark green shorts, a white cap with the letter "K" written on it and light blue shoes.
A ne'er-do-well, Kenichi is quite clumsy and often messes up. He does very poorly in his studies and often gets low marks. He doesn't follow his parents' advice properly and often gets into trouble. However, even though he doesn't study well, Kenichi's heart is in the right place, and he helps people when they are in need. He is mostly Kemumaki's prey.
Kenichi is also clearly in love with Yumeko, though she rarely sees the good in him. A long-time homework hater, Kenichi turns to Shinzo and Shishimaru when Hattori refuses to help him. However, he is a troubled character - innocent, insecure and lacking confidence.
Kenichi is also bugged by others, particularly Hattori, to be a "man". This just goes on to show that Kenichi is mostly the butt of a joke.
He's also quite workshy, and frequently asks Hattori to help him in any situation. He frequently tries to cheat with the help of his foster brother, just to prove that Kemumaki is a loser.
Kenichi loves his family, as anyone would. Despite his parents repeatedly telling him off for getting low marks, they genuinely care for him.
Shishimaru, Kenichi's gluttonous pet dog often annoys Kenichi with his greediness. However, he and Kenichi are close friends and once lived together in a giant pipe.
Kenichi has a serious crush on his classmate, Yumeko Kawai. She is unafraid to reciprocate these feelings, though she gets jealous when he talks to other girls - he once got slapped by her when she saw him talking to Kemuzou Kemumaki who was in disguise.
Kenichi has a very dangerous feud with Kemumaki and Kagechiyo - it started when he kept winning Yumeko's heart and being a goody-goody two shoes in front of others - while making Kenichi's life a misery. Eventually, Hattori came to his aid. They both fight Kemumaki and his cat Kagechiyo together - though Kenichi does join forces with Kemumaki at times to solve problems.
One day, while watching a ninja movie on TV, he encountered Kanzo Hattori, a real ninja, at his window. His family decided to foster him and from that point onwards, they became friends.
- "Yahoo, we did it!" (the first line, said while watching television)
- Kenichi dislikes carrots and tomatoes.
- Kenichi spoke the very first line in the show.
- Life Skills: Kenichi isn't very good at life skills, possibly because of his lack of confidence.
- Sports: Kenichi isn't very good at sports, also because of his lack of confidence.
- Photography: Kenichi is a pretty good photographer, however, sometimes, his pictures don't turn out well.
- Kenichi or Ken'ichi is a common masculine name in Japan. According to Mrs Mitsuba, it means "the healthiest one".
- Mitsuba either comes from Mitsuba Mitsuba (aka Japanese parsley) or partly from Mitsubishi, a Japanese carmaker.