She has a horrible gambling addiction. Manipulative and analytical, skills she gained through said gambling.
Yugao is aloof, can come off as cold, and relatively does not show off emotion. She does not hold back her opinion when speaking casually, but against opponents she will lie to her heart's content to get the result she wants. She is known for being very manipulative and conniving, skills that make her a master strategist which carried her up to her position as Mizukage. Though she does not show it, she cares about her village and it's people and knows what to say to provoke her subordinates to do their best. She has a gambling addiction which can be blamed on her family. She is quite egotistic yet proclaims that she hates herself.
Nuibari. The blade itself assumes the form of a narrow longsword that greatly resembles a large needle, with a long length of thin wire mirroring thread, tied to the eye located at the base of its hilt. This sword is said to possess the ability to pierce all and stitch them together, demonstrated through its ability to effortlessly penetrate multiple targets in a single thrust and then quite literally stitches them together in substantial bundles, by simply pulling the attached wire taught. A capable user can even throw the sword with the intent of piercing a line of multiple enemies, before catching the needle at the other side and repeating the process at different angles, in order to create knots of corpses with the wire passing through the entirety, effectively creating bundles of bodies at various points along the length of the thread.
The thread is made of chakra from the user, and can only be cut by Nuibari itself.
After Kabuto was defeated and peace returned to the world, the sealed corpses he revived were released and free to return to their villages to live out the rest of what their natural lives have been. Yugao trained under Kushimaru Kuriarare, one of the revived corpses, at the young age of 9, learning to wield the Nuibari. Unlike her sensei, her chakra was not nearly as vast and it took her 6 years to master the Nuibari completely. Kushimaru only accepted her as a pupil after she won a bet with him, she would write down exactly how a match of Shogi will go, each and every move. If she won, he'd have to teach her, if she lost he could take her life. She won, impressing the swordsman so he took her as his pupil. She made up for her lack of chakra with her immense intellect, often beating Kushimaru in occasional Shogi games which led to her repeating an intense workout regime.
As a child, Yugao wore a mask to conceal her face at all times, when asked about it she claimed, "a face can show your moments of weakness and tell your opponent what you're thinking." She now wears the mask 24/7, never taking it off, not even to sleep, the only time she takes off her mask is to eat and drink, or when using her facial expressions to manipulate. She grew up in a family full of gamblers, and good gamblers at that. The village speculates this is where she got her skills at reading people and manipulating them. She enrolled at the Ninja Academy after growing bored of gambling with her family all day. She wasn't considered a prodigy at all however, even though she rose up the ranks quickly. Her amount of chakra was below average, and her ninjustsu skills were minimal. Genjutsu, Kenjutsu, and her strategic skills are what has helped her move up. Though she was a ninja, she never gave up her gambling habit.
The last Mizukage had died 5 years after she was promoted to Jonin. The Mist's council of elders decided that the position should be left to someone who is smart and strong, naturally. They gave all the Jonin and ANBU a written essay exam based on strategy claiming that their status as a ninja would be revoked if they did not pass. Next they had a physical exam, pitting them up against eachother again threatening their status as a ninja. Yugao exceeded on the written exam and made it to the semi-finals, defeating everyone through her sharp wit. She could have gone through more, but she had already used up the rest of her chakra. The elders decided she was an excellent candidate, and gave her the title. She refused it at first, not wanting to do all the paperwork, but after a compromise she accepted. While she does paperwork, she often complains about how she could be out gambling.