Nope, this game is faction locked. Territory war is a big part of PvP in this game and exists through castle sieges.
Not so much "big part of PvP" on the JP version ... close to zero even, for faction / territory pvp
I've rarely seen a "faction pvp mmo" with so little little impact on the map and no real interaction between factions
Hope they will change this (miraculously) for Steam Version