Proposal by SP19XX:
Spell Cost: 6
Numenorian Heritage
The blood of the ancient Numenorians lies strong within the people of Arnor, expanding their lifespans, and is most prominent in their Kings. Units of Arnor will regenerate their health while out of combat. In the presence of their Kings, the regeneration is enhanced by 10%, stacking up to a maximum of 30% in the presence of Araphant, Aranarth or Arvedui.
A neat little suggestion from SP19XX while discussing the upcoming 4.5 patch on the unofficial Edain Discord Server. He suggested the the central spell for Arnor be the "Bloodline of Numenor" ability (currently far left end of the tier 2 branch). He thinks that it would fit great with the theme of Arnor specifically connected to their long life and connection to the Edain, in addition it would give an appropriate place for a powerful spell such as that one. I agree entirely with that proposal, it's short simple and neat and gives Arnor its own touch.