Sieg? So is that the official unofficial name for the main character I was wondering? I don't think the guy has brain problems he just doesn't care about it. I mean its one thing to go look for your parents if you never seen or met them but the fact that you are from another world even if you wanted to you couldn't go. I believe the castle fortress ruins were the only thing that One King brought to the current world after he destroyed Sieg's fathers world. Once Sieg and Atrie had the conversation about the hero from the chronicle (Sieg's father) and that Sieg couldn't go through any gateways except the one he came through when he was baby would be impossible because the world no longer exists and the only part of that world that does exist is the castle and its gateway and by him going through the gateway its only natural he ends back up where he started.
"Even the dead reveal their secrets to me." Yuber
"I have not lived long enough to become a myth." Chris Lightfellow
"They betrayed us and fled. Cowards." Zegai