Bloodthirst

Bloodthirst is a skill introduced in Fire Emblem Fates it is the Personal Skill of Peri.

Fire Emblem Fates
If Peri initiates an attack on an enemy and kills them, her Strength, Magic, Skill, and Speed increase by 4 until her next turn. Bloodthirt's stat bonuses do not stack with the effects of Rally Strength, Rally Magic, Rally Skill, and/or Rally Speed.