Midjourney is excellent at taking an image and using it’s features to create a new image. I would be careful using a Disney Pixar image as the base of your artwork. Copyright is going to be tested in the future.
Hiei is a character from the popular anime and manga series “Yu Yu Hakusho”. He is known for his short stature, black spiky hair, and his Jagan Eye, which is usually covered by a white headband. He is a skilled warrior with demonic powers.
“Wearing a Karate Gi”: A “Karate Gi” is a uniform for training in Karate and other martial arts, made from heavy white cotton. This suggests that Hiei is dressed in a traditional martial arts uniform, which is somewhat unusual as he’s typically depicted in a black, sleeveless outfit.
“Using black magic”: In fiction, “black magic” often refers to supernatural powers or magic for evil and selfish purposes. In the context of “Yu Yu Hakusho”, this could refer to Hiei using his demonic energy or techniques for combat or other purposes.
So, the image description implies a depiction of Hiei Jaganshi from “Yu Yu Hakusho”, dressed in a Karate Gi, performing some sort of dark or demonic power.