Kojiro wouldn't say that he was someone overprotective. He was basically the opposite, since he loved to have a new lady in his arms every week, or... hell, why not a new one every night? The whole 'settling down' wasn't really something that called for him. He preferred to be free, and do as he pleased, without ever needing to ask anyone for permission. Where was the fun in having a ball and chain that kept you down?
That was... until the Adam accident.
The moment where, before his very eyes, Kojiro saw that he failed. He saw, in slow motion, how the skateboard was smashed against Kaoru's face. How the impact seemed to echo, or maybe it was his brain paying a trick on him. But he could've sworn that he heard everything happen over, and over, and over again. It had happened so fast, and yet so slow. One minute, he felt proud and smug, already seeing that he would have to buy a good bottle of wine to celebrate... the next one, Kaoru was motionless on the ground.
Kojiro changed his mind after that day. He was protective. Very damn protective.