Xen's Links
During his days at the Unown Force, he found Erin kind of vulnerable due to their clumsiness despite being a cheerful young unown. He was right on which it made himself worried. Xen saw what Erin's been through after finding them.
The only unown close to Erin, both have some opposites yet their relation aren't surprising upon knowing they're siblings.
Xen has killed many, Erin has killed none.
Xen doesn't remember Oz that much since Xen was amnesiac upon joining the Unown Force, neither he cares about the mythical pokemon unless he knows something about Xen.
Oz never forgets the day both of him and Xen met before they got accidentally dragged to another world, due to their world infested by Ultra Beasts. He lost sight of Xen upon arriving.