You probably misunderstood/misremember, while it's true that I am against all forms of NTR, Sona is not Kiba's LI, nor the other way around. I probably said Saji, but under a different context since from day 1 I've always said Sona will be an (optional) heroine. It will pretty much go like this: At some point during the story, you will unlock a side quest to defeat Sona in a chess game (actual minigame), and if you do, you begin her romance. For those who don't know how to play Chess, I'll add a way to skip the minigame (similar to how you can skip battles).
If I had to guess, you mixed up Tsubaki with Sona.
I remember someone once asked about Tsubaki, and I said she's interested in Kiba already.