Disclaimer: Hikago isn't mine.
The first time Shindo willingly brings up Sai without being goaded into it, they're playing a casual game at the salon. It's an excellent game, one of the better ones they've created together, and Akira's solidly in the lead.
Everything's been going so well, and the game's been playing out so beautifully, that he's almost expecting it when Shindo starts to make one of those astonishing, captivating Sai-like plays. Akira feels his breath catch in his throat when he sees his rival's intention--it's a brilliant move, cutting him off on two fronts simultaneously.
Except Shindo doesn't take his fingers off the stone--he freezes, eyes scanning the board, and suddenly he's jerking his hand to the left, making a move Akira can't begin to understand. And Hikaru makes another odd play, and then another, and suddenly Akira sees it, sees the outline of the shape to come--too late to stop Hikaru from destroying one of his eyes, too late to maintain his lead.
It's no more devastating than the original move would have been, and Akira can only stare at Shindo for a moment and wonder just why it had to be the one play and not the other.
"Sai would have gone where I was about to go," Hikaru says with an inexplicable certainty, somehow sensing the unvoiced question in Akira's mind. And there's something strange and painful in the way he says it, in the way he adds, without ever looking up from the board, "But Touya, I'm not Sai."