The original idea belongs to Love Psycho and the fanfic Ten facts about Rin Okumura (And the secrets that go with them).We may or may not continue this in a sequel(s).This relies on headcanon. This was written and posted by Mod Dipper. Also, TEAM TRANS BOY RIN OKUMURA FOR LIFE.
Rin Okumura can always tell when someone is lying. Always.
It's part of being a demon, every demon has a talent unique to their bloodline. When bloodlines merge, the new demon had a new talent. This is something known by all , for a large portion of his life, Rin didn't know he was half demon and had no one to explain any of his more demon aspects.
But he did know when someone was lying. He knew his teacher was lying when she said she loved her husband. He knew the teenager who came to church with his family was lying when he said he was clean from the drugs. He knew that people were lying when they said that because he had girl parts, he was a girl. He knew that his daddy lied about what he did and where he was going, and when Yukio went with him, he lied too. He knew that the people who called him demon were lying, but so were the people who called him human.
He didn't know how he knew this, but he did.
Rin Okumura can always tell when someone is lying. Always.