Kenji is the husband of Rei Nakano, father of Kasumi Nakano, and small time fisherman from the Northeastern coast of the Commonwealth. He had helped Nick Valentine out on a previous investigation, but was shot in the hip during the case. He contacts Ellie Perkins, Nick's assistant at the agency, to hire Nick to help find his missing daughter.
The following is based on unverified behind the scenes information and has not been confirmed by canon sources.
Kenji may be an easter egg/homage to an old SEGA genesis game called Bimini Run. When first encountered you can hear him say "Dammit. Come in! I know you're listening on the other end! Where is she? Where's my daughter!? come in!" as he's talking into the radio receiver. In the game Bimini Run you were constantly contacted via radio saying "Kenji, come in!"
End of information based on unverified behind the scenes information.