Kelvin forces Efil to take two specific skills: Double Skill Points and Double Experience Gain . This is a "late-game" build—she starts weaker but will eventually outscale almost any other character.
Kelvin purchases her and immediately uses his MP (Mana Points) to heal her curse, revealing his kind but pragmatic nature. He then begins training her in archery and fire magic. ⚔️ Combat & Mechanics Guide Kuro no Shoukanshi Episode 3
Check out the detailed stats for Efil and Kelvin on the Black Summoner Wiki. Kelvin forces Efil to take two specific skills:
Episode 3 dives deeper into how "Skill Points" and "Growth" work in this world. Kuro no Shoukanshi Episode 3