Verdure Elder Elikia:
Kelbim is a high officer of the Embryo. He isn't inside the Atelia Fortress all the time, but he does come from time to time to manage it. There are many obstacles you must go through to get to the castle. First, you must defeat the Atelia Trial Guardian Captain who guards the gate to where Kelbim is. That's how you'll be able to open the gate. This isn't the end.
That place makes people who know each other fight. It might be because of the Atelia's effect. Anyway, you have to be wary of everyone inside. There's more to that, though.