We need a champion completely built around the idea of transferring damage to themselves

Warlock has a spell that links everyone in an aoe. All the linked targets take damage equal to 20% of the intended target. It essentially makes aoe damage iwin damage. There are several design problems with the spell even it feels like you are a god when you destroy the enemy and there are ways to counter it, but that's not the point. I'm describing Soul Link because I want you all to think about it in reverse.

Your champion has an ultimate that links their health with everyone else's in a small vicinity. When they take damage, 50% of the damage is instead transferred to the caster. That means the champion can soak a lot of damage in a short period of time except that it kills them if they are too squishy. So unlike Warlock's E where it's basically just "here's more aoe damage for your aoe and single target damage," this ult makes you stop and think, "if I ult now, I could die, which prevents me from doing more cc in the future and therefore unable to peel for my adc. However, if I don't ult now, my adc could be low enough that my reflexes can't save them if the enemy manages to break through our wall."

Braum doesn't really fit since this champion is all about transferring damage whereas Braum is about blocking spells period.