Lan Xichen defied his uncle only once in his life.
It was after Wei Wuxian died, right after Wangji was punished, when Lan Qiren ordered Wangji taken to the Cold Cave right away. It was then that Lan Xichen stepped between his uncle and his little brother and said, quietly but firmly, no, not like this, not until he’s healed, not until he’s okay…
Because Wangji couldn’t even stand up on his own, because his back was quickly turning from angry red to sickeningly black and blue, because his skin was split and broken by the discipline whip - just looking at his little brother’s wounds turned Lan Xichen’s stomach. This, this wasn’t a just punishment for perceived misdeeds, this was a retaliation, done in anger.
And when Lan Qiren snapped at him, when he accused Lan Xichen of always taking Wangji’s side, when he blamed Lan Xichen’s lenient attitude towards his little brother for what Wangji’s become, defiant, reckless, foolhardy, Lan Xichen stood there, shielding Wangji, and stared at his uncle with his heart beating hard because his upbringing was yelling at him to obey, obey, obey…
But he did not. For once, for his little brother, Lan Xichen defied his uncle.
And when that night Wangji got a fever, when infection spread through his body, quick as a wildfire, despite their healers’ best efforts, when his temperature rose so high that he started seizing in Lan Xichen’s arms, when Lan Xichen took him down to the Cold Springs and waded in, and holding Wangji against his chest, he washed his wounds, again and again and again, tirelessly and with much care - Lan Xichen knew he had done the right thing.
When Wangji then finally healed, when he finally got well enough to be sent to the Cold Cave that was to become his prison for the next three years, when he calmly accepted his fate as was his wont and Lan Xichen bade him a sorrowful goodbye because his heart was breaking anew for his little brother - Lan Qiren didn’t even look them in the eye, either of them, his demeanor was as stoic as his nephew’s. The terrible mistake that he almost made and which almost cost Wangji his life didn’t change anything, anything at all.
And Lan Xichen’s life became a little sadder that day, his opinion of his uncle a little more sober… and his determination to protect his little brother all the more firmer for that.