So we all know Brian right? He betrayed Phoenix and afterwards was nowhere to be seen. Well I want to give my thoughts on Brian's motives, thoughts, and where he is now. Also some facts about grey wind as a treat.
So Brian was 15 when he met Aphmau, he was sent to the guard academy as soon he was 6. He was expected to be top of his class by his father. When he finished his training he wasn't even in the top ten, but still went to train under Garroth. The first week he came back, the old lord died. So when Aphmau comes, he watches as things are fixed up but at the same time a ton of bad things happen.
Brian looked up to Zane when he first came, with Zane being a High Priest, and Brian raised by a very religious mother, he looked up to Zane. Zane used that to his advantage. Zane used manipulation to try to sweeten Brian up, due to Brian being young he bought it hook line and sinker. Zane told him whatever he did was in the name of Irene, and he cared very deeply for every village in Ru'an. Right before the Alexis incident, Zane told him that he could allow him and his family a much better life, all Brian had to do was follow him. Brian didn't answer right away, so Zane gave him time to think.
When right after Alexis woke up, Brian got a letter from Zane. Zane used his manipulation once more to convince Brian that Aphmau was a bad guy. Zane did this by stating all the bad things happen in the village because she showed up, and if Aphmau joined O'kasic then everything will be peaceful once more. Brian just wanted things to be peaceful like when he was a kid, so he agreed to work with Zane on the condition that Zane will leave Phoenix alone afterwards.
After the war, Brian used the fact that everyone was recovering from the war to flee. He ran home when no one was watching and grabbed anything he needed to restart his life. Later after Aphmau's group went to the Irene dimension, he left at night. He would run to Tu'la and live in a small village for the rest of his life. He did leave a letter for each member of his family. The letters explained what he did, why, and that he was never coming home. Dale didn't read his letter by choice, Molly read her's and cried for days on end, Alexis didn't really remember Brian so never cared to read it.
Grey wind stayed in Phoenix Drop during the 15 years time skip. Staying with Dante cause Brian left grey wind behind. Grey wind would acted as a guard dog by the pier, barking when grey wind saw a ship. Grey wind did end up dying before Aphmau and crew came back, sadly it was due to bandits.