I don’t think any subtext made it into the books, ha. I sort of sneaked it into a long and rambling explanation about Riko. The short answer is: Kayleigh had something Tetsuji wanted, and Kengo decided to acquire it for him the cleanest way he could.

“But Tetsuji was still responsible for Kayleigh’s death, in a roundabout way, because he opened his mouth about her to Kengo. He wanted more of his brother’s money so he could invest in a new program for the Ravens, and he told Kengo his plans for Riko. He also told him about Kevin. Two days later Kayleigh was dead, and Tetsuji had both his money and his second pet project. Tetsuji immediately handed Kevin off to Riko. It took him a few years before he spoke to his brother again.“