Kojiro is extremely loyal to Kaoru and likewise for Kaoru. Kojiro has a "papa bear" mentality and appears as a father figure to the younger boys, offering advice and noticing when things are off about them. He is very open-minded and kind towards the younger boys trying to help them whenever he can.

He is a skilled skater and member of a street skating gang called “S”, which he leads. Joe's character is often depicted as being calm and collected, with a dark past that has shaped him.