Kenichi Mitsuba (三葉ケン一 Mitsuba Kenichi) is a 12-year-old boy who goes to primary school. His parents are Mr and Mrs Mitsuba. He often gets low marks in his exams. He is in love with Yumeko Kawai, however arch rival Kemuzou Kemumaki is always after her.
Kenichi is of average height and has a slightly stocky build. He wears black square shaped spectacles and has small black eyes. Most of the time, he wears a light blue T - shirt with red and yellow stripes on it, dark green shorts and a white cap with a "K" on it. His pyjamas consist of a striped blue and grey nightshirt and matching trousers.
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 complex 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.
Kenichi loves his family, as anyone would. Despite his parents repeatedly telling him off for getting low marks, they treasure their son and would be devastated if anything happened to 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 a 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 encounters Kanzo Hattori, a real ninja, at his window. His family decides to foster him and from there, they became friends. He 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.
- "Yahoo, we did it!" (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.
Kenichi or Ken'ichi is a common masculine name in Japan.
Mitsuba either comes from Mitsuba Mitsuba (aka Japanese parsley) or partly from Mitsubishi, a Japanese carmaker.
Kenichi was voiced by Masako Sugaya.