The Concord of the World Tree is an organization seeking to unify the shards through the transplanting of flora and fauna between the shards (hoping the similarities of bio-sphere will draw the many worlds together again). On their home shard of Ydrassa, there are sites where the forces they cultivate through the great trees are harnessed and enhanced.
(an) Sebastian, in the 15th century, was born in a catholic family but was sold to work in the mines. His only friends was some cats. But the cats were taken away or killed by his "superiors". One day he just lost his mind and killed everybody. He escaped and came into a church to ask a priest why God lets all this happens. The priest was afraid by all the blood Seb had on him, so he killed him too.