Spiritual Host (3.5e Trait)
From D&D Wiki
There's something inside you, sealed into your very soul. Be it good or evil, there is definitely a spirit sealed inside of you. And it wants out. More than anything you know.
Benefit: Spiritual Hosts gain the subtypes (except Incorporeal), immunities, and Damage Reduction of their Spirit (if any).
Drawback: Spiritual Hosts are vulnerable to many of the same weaknesses of their sealed Spirit (For instance, a character with a Fire Elemental sealed inside of him would have Vulnerability to Cold). In addition, if you are killed (brought to -10 HP or less), the Spirit explodes forth from your body and must be defeated before you can be raised or resurrected.
Normal: You're not a direct rip-off of Naruto Uzumaki or whoever else went through this.
Roleplaying Ideas: Spiritual Hosts are either revered or hated beyond their wildest dreams, depending on the context of how their "Guest" was sealed inside of them and the alignment of said Spirit. For example, if you're the host to an Elder Evil that ravaged your village a long time ago, people who know about it will hate your guts. But, if you're playing catcher to a heroic dragon of ancient times, you'll need a rape whistle and a lot of bodyguards just to keep your fangirls at bay.