Kenji is a young boy with gold eyes and short blond hair that reaches past the nape of his neck. His bangs are gathered at the center of his forehead and he has freckles across his cheeks.
He wears blue overalls that are cuffed and a black belt around his waist. His overalls are worn over a loose beige shirt that has tattered sleeves. He wears a black undershirt that has sleeves ending a little past the elbows. He wears an old straw hat around his neck. He usually goes barefoot but is sometimes shown wearing sandals.
Hailing from a small rural village, Kenji is a simple, but carefree and hospitable boy, who never fails to greet people with a smile on his face. It's because of this welcoming disposition that makes him very popular with the residents in the city.
He carries an exceedingly optimistic outlook and always believes in the innate sincerity of others, regardless of what they may appear, say, or do. His obliviousness to the dangers some situations pose may be attributed to his rustic upbringing, but it's a mentality that has aided him in several investigations, given his high track record in solving difficult cases.
Because Kenji is from the countryside, he is also unable to comprehend basic urban concepts such as money and often has to rely on his rural instincts. This leads to more peculiar "methods" of the resolution, such as using his ability to beat culprits into submission, an act that has yielded him a fearsome reputation amongst the more suspect groups in the area.
Kenji's ability, Undefeated by the Rain (雨ニモマケズ, Ame ni mo Makezu?), grants him superhuman strength. This lets him perform feats he normally wouldn't be able to do, such as lifting cars with ease or pulling street signs out of the cement. He can even rip a steel door from the same type as is used in high-security bank safes from the wall. It also seems to grant him superhuman durability, as he was attacked in the back of the head with a lead pipe and suffered no ill damage whatsoever (such a blow could damage or kill a person) and he mentions getting kicked in the head by cows all the time and seems to have survived with little to no damage.
The catch to his ability is that he is only able to use it on an empty stomach, and will fall asleep after eating.
Until Yukichi Fukuzawa found him and recruited him into the Company about two months earlier, Kenji had been living in a rural village named Ihatovo where he herded cows with his family. He had been living without any forms of phones and electricity, and the concept of money was new to him as the inhabitants of Ihatovo only bartered.
Kenji also states that the police in his village wasn't as busy as the ones in Yokohama, as the criminals in Ihatovo simply got tied up and thrown off a cliff.
- (to Atsushi Nakajima) "Whether in a town or a village, whether toward a cow or a person... If you're sincere toward others, they'll respond in kind. That approach has yet to fail me." 
- (to Atsushi Nakajima) "Oh, I just love cows! Raising them, working with them, eating them too!" 
- "Undefeated by the rain, undefeated by the wind, undefeated by metal pipes, knives, or aluminim bats, strong in body, undefeated by desire and certainly without offending others, always with a quiet smile to be such a person. "
- (to his fellow Agency members) "Let's live, everyone, beyond the storm and beyond the dawn, because in the end, on this spinning rock called the Earth, we must keep living."
- His family's motto is "If cows defies you, strike it with something handy." 
- He along with several other characters made a guest appearance in the mobile game Love Heaven as limited-time characters.
- The name of the rural village where he lived, Ihatovo, is a reference to the fictional land Miyazawa created, basing the name off his beloved Iwate Prefecture. In fact, the name lends from Esperanto.
- Kisho Taniyama has taken to calling him MiyaKen