What an interesting side story!
Tokuya wasn't some jerk ass yankee manipulating Kouki. He found Kouki likeable and tried to cheer him up in his own way.
What I'm wondering is what did Akari see in Kouki? Kouki is 2 years younger and acts like a brat at the time, so why did she hang out with him to the point of going out? Was she really that friendless as her big brother said?
Really, though, it would have also been interesting to see more interactions with that big yankee.