Essence Theft (Ahri Passive)

When you kill a creature of CR 1/4 or higher, you may use a bonus action to siphon its life essence, restoring your vitality. Roll 1d4 and add the creature's CR (rounded down). You regain hit points equal to the result. The creature this was used on cannot be brought back to life by simple means, since their essence was captured. (DM's discretion as how much effort is needed to bring them back.)

Cantrip Upgrade. The healing increases by 1d4 when you reach levels 5 (2d4), 11 (3d4), and 17 (4d4).