Not exactly what you stated, but it sorta reminds me of the time with Titania in Part 3 End-Endgame.
I pulled a risky move to go kill off Laura since she just recently used the sleep staff on one of my units. (I was regretting ever assigning it to her...) Laura positioned near the top of the map and there were still plenty of enemies remaining around from where she was.
With my turned finished, equipped with a brave lance, Titania annihilates anyone (IIRC) that comes at her during that enemy phase. Though, losing a bunch of HP in the process naturally. I can't recall what her HP was exactly, but it was not looking to good when Volug came at her.
With only 1 HP point remaining after Volug attack....she uses Sol and kills. Keeping her alive throughout the rest of the turn.
Gotta love those paladins in Fire Emblem.