I feel like this is trying to do too much.
It fits in the same sort of niche as Knight's Vow and Zeke's convergence...honestly, it overshadows both of those things while also providing a murderous level of both offensive and defensive stats on top of giving an ally a GA.
Imagine a Zilean that built this and made his friendly Aatrox so immortal, he gets to rez FOUR TIMES (once from his own ult, once from Zil ult, once from GA, and once from SoulStone) in a single fight. That would mean Trox could go full glass cannon build in mid and literally never worry about feeding, even in a losing fight, because everyone will have to blow their cooldowns four separate times just for him. That's not even mentioning the shield passive, the extra damage from the explosion on it breaking, and the fact that despite building out of an AD item, Zilean still gets 80 ability power which is the same amount of AP as a gunblade or lich bane.
I do like the concept...but everything's really out of whack.
Try this:
Build Path:
+
+750 gold (total 2700g)
+50 Ability Power
+400HP
+300MP
+7% Movement Speed
UNIQUE Passive: Eternity - 15% of damage taken from champions is gained as mana. Spending mana restores 20% of the cost as heath, up to 20 per spell cast.
UNIQUE active: Soul Stone - Target an allied unit within 750 units of you to bind their soul to this item. The bound champion is set to receive the benefits of Phylactery until unboaund. (60s active cooldown)
UNIQUE passive: Phylactery - When the bound champion takes damage, 10% of the damage taken within the last 4s fills this item the next time the ally is out of combat, to a cap of 20% of their max hp. Should the ally take lethal damage, they are resurrected after 3s with the amount of hp stored in this item next to its holder. 3 minute CD on rez.
This will give you a more support based item that's still a solid pickup for AP players, it wont take away from your aesthetic but it will add to its complications by requiring your ally to leave combat to store their damage taken (and to take a lot of damage) before it does much, and it doesn't make anything too terribly overbearing.