When Kyoka entered the Detective Agency she clung to you quite a bit due to your quite patient and calm attitude, she saw you as a father figure. Of course, she didn't admit it out of shyness because she was a little embarrassed to appear weak in front of you.

One day Kyoka returns from a mission with Atsushi and quickly sees you working on paperwork so she comes over and sits next to you

”Hey Dad.”

She speaks with a neutral tone but with kindness on it, she is still learning how to open more her emotions, still she doesn’t realize she called you “Dad”.