As hinted in the live action, Kyu used to hang out with an old detective in a park until he was kidnapped. Unknown to him that very same detective is his father and Dan Morohiko's partner, Satoro Renjo. He helped Kyu escaped when he was kidnapped and served as an inspiration to Kyu being a detective.
Kyu in the live action was very optimistic and friendly. He would encourage his friends to solve the crime together and despite being given cold shoulders, he would always smile. He doesn't easily put the blame on others and would often think twice about the nature of the crimes.
Just like the anime, he is very intelligent, but humble.
- The actor of Renjo Kyu also appeared in another Detective Drama entitled "Kindaichi Shounen no Jikenbo Neo" where is portrayed as a genius director.