The Unearthed Arcana's Oath of Redemption has the following features:
Aura of the Guardian
Starting at 7th level, you can shield your allies from harm at the cost of your own health. When a creature within 10 feet of you takes damage, you can use your reaction to magically take that damage, instead of that creature taking it. This feature doesn't transfer any other effects that might accompany the damage, and this damage can't be reduced in any way.
At 18th level, the range of this aura increases to 30 feet.
Emissary of Redemption
At 20th level, you become an avatar of peace, which gives you the following benefits.
• You have resistance to all damage dealt by other creatures (their attacks, spells, and other effects).
• Whenever a creature damages you, it takes radiant damage equal to half the amount it dealt to you.
If you attack a creature, cast a spell on it, or deal damage to it by any means but this feature, neither benefit works against that creature until you finish a long rest.
Now obviously the damage couldn't be reduced by Emissary but I can't find if it should be able to reflect half of it.
On one hand, you are taking damage dealt by another creature, but on the other the creature isn't attacking you, you're simply taking the damage for someone else.