So that’s the reason why Ginga is the way he is. He was trained very well by Kou. Also, now see why they both bonded with Yuu. Kou gave Ginga so much of his bodily fluids that it changed him. I believe Kou was Yuu’s fated mate.
I’m glad Yuu chose Ginga and Kou and could bond with them, too. If he had chosen only Kou, Ginga would’ve been damaged beyond repair. Completely broken. So I am very glad that it turned into a poly love. Also, it is obvious that Yuu comes first for both Kou and Ginga in everything.
To clarify, they did not cheat on Yuu. They slept together to ease the heartbreak of Yuu constantly choosing anyone but them. They understood each other’s pain and heartbreak and sought solace from each other. Also, Yuu did find out about it at the doctor’s office and didn’t care. I think he was more fascinated by it. (⌒▽⌒)