Himiko is jubilant and charismatic. She is seen with a smile most of time and have an extremely effervescent and joyous expression. She also have a carefree nature to her as seen by how she does not mind calling someone she fights as a friend like Ochako Urararaka. Himiko is also sadistic when she takes pleasure from taking blood from Ochako in her battle. She also has a crush on Izuku Midoriya and seeing him as attractive. When she saw him after his fight with Muscular, she remarked on his beaten up appearance as something that is attractive to her. While she is carefree and happy at most times, she has a surprisingly violent personality as told by her crimes which involves murder and her desire to kill the Hero Killer even though she likes him.
Himiko first appeared at Tomura Shigaraki's base with Dabi as new recruits to the League of Villains. Tomura was not impressed by their praise of Chizome Akaguro. Tomura tried to attack them out of spite but his attack was deflected by their moves. Despite Tomura's hostile encounter, they were accepted into the League of Villains.
Himiko later appeared with a few other villains in the Vanguard Action Squad. Their objectives were to attack the Yuuei students at the camp while they trained. During the attack, Himiko encountered Ochako and Asui. She had a device that was being used to take blood from her targets. As the fight continued, Himiko held a conversation with Ochako about a crush that she had. As the confrontation continued, Himiko retreated in the woods as the other Yuuei students came to their location. As she left the scene, she glanced at Izuku in his beaten up appearance from Muscular and blushed. She made it to the exit point of the forest where she waited for a villain to bring Katsuki Bakugou with them. Black Mist appeared and he was able to help the members of the Vanguard Action Squad retreat from the scene and capture Katsuki.
They kept Katsuki under them intending to make him join the League of Villains. With the help of the heroes and the U.A students, they were able to retrieve Katsuki from the villains. All for One also transported the villains out of the way to deal with All Might.
Himiko later took the DNA of a girl called Camie to infiltrate the U.A students during the Hero License Exam so that she could get close to Midoriya and obtain his DNA. After getting his DNA, Himiko went back to the League of Villains without getting caught.
Powers and Abilities
Transform: Himiko's Quirk allows her to take the physical form of another person, as well as intimate their voice. She pulls this off by ingesting the blood of the person she's stabbed. She needs a large quantity to pull this off, however, as a small stab from Ochaco Uraraka arm was not enough. She can also shift between disguises, if she's consumed more that one person's blood, as shown when she changed from Uraraka to Camie. Her Quirk does have limits though; for one, she cannot take Quirks of the people that she disguises herself as. Another point to bring up is that when she transforms, her clothes are absorbed into the new clothing that her Quirk creates, so when she transforms back to herself, she's left being naked.
Stealth: Because of her Quirk, Himiko is capable of pulling off great stealth techniques, making her an incredible stealth agent. When she was disguised as Camie, it was implied that she fooled her classmates for three days, although one of them noted on her odd behaviour. She also had Izuku believe that she was the real Camie, and that Transform was Camie's actual Quirk.
Overall, Himiko is a crafty villain. While she has no clear fighting style, it is clear that she's a dangerous fighter, as she was shown to fight rather aggressively against Midoriya during the Hero License Exam arc. She is quick and agile enough to keep up with the likes of Pro Hero Eraserhead, and was even able to get a quick stab on his shoulder. She also fast reaction timing, as shown when evading sneak attacks from Ochaco and Hanta.