Susamaru was shown to be rather playful, yet very brash and quite immature while almost always smiling and always enjoys and accepts a challenge. Her pet phrase is "what fun this is" and she will repeat this constantly if engaged in bouts she deems amusing. Her immaturity is a stark contrast to Yahaba's seriousness.
She was fanatically loyal to Muzan and battled to her best ability in the hope of killing Tanjiro and taking Tamayo hostage for her master. Just a girl whose been brainwashed.