Shizune

is a jōnin-level kunoichi of Konohagakure, as well as the Fifth Hokage's assistant.

Background
Shizune is the niece of Dan Katō, a renown shinobi of Konoha. Some time after Dan's death, Tsunade, his love interest, left Konoha, and Shizune went with her as her attendant and apprentice. The bond between Tsunade and Shizune is strong and, above all, Shizune sees her purpose in life as caring for Tsunade.

Personality
Unlike Tsunade, Shizune is level-headed, practical, and a rational thinker. As a result, she is the one who tends to stress over details, such as Tsunade's tendency to gamble and to think with her heart. She often gets comically worked up over any irrational decision Tsunade makes. Shizune also looks after Tonton, Tsunade's pet pig. She is not the type to tire easily and is very energetic and efficient while acting in her capacity of Hokage's Assistant, often urging Tsunade to finish the paperwork in order to avoid mountains of unsigned documents later on. She is often seen asking Tsunade questions about what to do with the village and the shinobi on missions.

Appearance
She has shoulder length black hair with bangs and dark eyes. Normally, Shizune is seen in a long blueish-black kimono with white trimmings, held closed by a white obi, and open-toed sandals with low heels. Shizune has also been seen wearing the standard Konoha shinobi outfit when deployed on missions with distinct over-long sleeves.

Abilities
As Tsunade's first apprentice, Shizune is a very capable jōnin-level shinobi. She is quite fast and equally fierce and precise in her attacks during battle. Her skills in battle mainly revolve around her use of poison techniques. Her chakra control is also great enough to do even the most complex medical ninjutsu. Her skills were also great enough for her to be put in charge of the Logistical Support and Medical Division of the Allied Shinobi Forces in the Fourth Shinobi World War.

Medical Ninjutsu
Shizune is noted to be a very talented medical ninja, in Konoha rivalled only by Tsunade herself and Sakura Haruno, another student of Tsunade's. Her training has blessed her with excellent chakra control, which is the primary reason she was assigned to lead the sealing of the Three-Tailed Giant Turtle. She demonstrated her great medical knowledge when she lead a group of medics in healing Neji Hyūga, even though she had only recently returned to the village after many years of wandering the world with Tsunade. This was again seen when she was put in charge of the autopsy Konoha performed on the Animal Path that Jiraiya had killed.

Poison Techniques
Shizune has rarely been seen in battle, but from what has been seen of her skills thus far, it appears that her techniques are mostly based solely around poison. Being a medical-nin, she has to keep her distance in battle, making sure not to injure herself so she can be of use in healing her team-mates later.

During her battle with Kabuto, Shizune is seen using Poison Mist, which creates a thick cloud of toxic gas capable of being fatal even if only a mere whiff is breathed in, as noted by Kabuto. She also uses poisoned senbon in a variety of ways, including firing them from a concealed wrist-mounted device and spitting them out of her mouth. Kakashi Hatake mentioned that Shizune was responsible for instructing Sakura on how to imbue her weapons with poison.

Search for Tsunade Arc
When Orochimaru came to Tsunade years later in an attempt to get her to heal his arms, Shizune attempted to persuade Tsunade against it, even trying to convince Tsunade to kill him with her assistance. When all attempts to persuade Tsunade failed, however, Shizune tried to use force to stop Tsunade from helping Orochimaru, although Tsunade easily defeated her. She later fought Kabuto Yakushi in an effort to protect an incapacitated Tsunade and Naruto Uzumaki. Despite Shizune's efforts, Kabuto proved too much for her, as he managed to dodge her attacks and incapacitate her, too. Shizune was able to heal her legs, and left the field of battle with the unconscious Naruto as the three Sannin prepared to conclude their battle. She then returned to Konoha with Tsunade after she accepted the office of Hokage.

On the way back, the group stopped in a hot springs town. When Senta and Bunzō had stolen the First Hokage's necklace which was currently worn by Naruto, the two plot to blackmail Tsunade to give them the money she owes their boss. When Shizune found the note, she couldn't find Tsunade anywhere which left her the choice to use the Transformation Technique to pose as Tsunade. When Naruto and the Akagi brothers stole the bag, Shizune in Tsunade's form goes after them. After Shizune took down Naruto, the Akagi brothers discovered that there's no money in it. Just then, the real Tsunade arrived and recognized Shizune in disguise. With help from Jirōchō Wasabi (whom Tsunade encountered in the casino), Tsunade explained that she already paid her debt to the Akagi the year before.

Sasuke Retrieval Arc
When Tsunade took on the title of Hokage, Shizune led a team consisting of Genma Shiranui, Raidō Namiashi, and Iwashi Tatami to compensate for the lack of manpower caused by the Invasion of Konoha. When Genma and Raido were defeated by the Sound Four, Shizune healed their wounds. Later, she was seen leading a medical team charged with regenerating the wounds of Neji Hyūga.

Anime Filler arcs
She appeared in almost every filler arc as Tsunade's attendant and secretary. During the Mizuki arc, she was defeated by Mizuki, who used her guise to lead Naruto and Iruka into a trap.

She was with Tsunade during the Land of Vegetables crisis. When the uprising in the Land of Vegetables and the caravan that Naruto Uzumaki, Chōji Akimichi, and Hinata Hyūga were guarding was connected, Tsunade sent Shizune to gather every available ninja and head over to the Land of Vegetables immediately. While Naruto was fighting Renga, Shizune, Shikamaru Nara, and the ninjas sent with her rescued Chōji, Hinata, and Yurinojō from the ninjas on Renga's side.

Part II
Shizune appears frequently in Part II, often being nearby when Tsunade is issuing orders.

Sasuke and Sai Arc
She began to grow concerned by Naruto repeatedly going up against members of Akatsuki, and reported this to the village elders. Although Tsunade was able to reach a compromise with the elders, Shizune doubted Tsunade's judgement on this matter, but she seemed to regain faith later on.

Three-Tails Arc
In the anime, Shizune was assigned to help seal the Three-Tailed Beast, joining the sealing team along with Ino, Sakura, and Hinata. Seeing the beast's sealing as a way to stop Akatsuki's plans, Shizune took charge of the process, instructing the other members in order to speed along the process. The sealing was repeatedly interrupted by Guren and her men, however, and the sealing was instead left to ANBU members.

Tsuchigumo Kinjutsu Arc
In the anime, Team Kakashi, while under Yamato's command, is sent to aid the near-extinct Tsuchigumo clan in guarding its dangerous forbidden jutsu from enemies. Later, while Shizune is doing her usual duties as Tsunade's assistant, Team Kakashi sends word to Tsunade about plans to destroy the forbidden jutsu with the clan's consent. Shizune wonders what Tsunade will do.

Invasion of Pain Arc
After Jiraiya was killed by the Akatsuki leader, Pain, Shizune was left in charge of examining the body he had captured. When Shizune discovered that the piercings on the body were chakra receivers, she was given ANBU escorts to ensure she could share the information with as many people as possible. She meets up with Inoichi, but before they could begin to collaborate, Shizune was captured by the Human Path. It read her mind to find out that Naruto was at Mount Myōboku, and then removed her soul, killing her. In the ensuing destruction, her body was kept safe, and was later revived by Pain's resurrection jutsu.

Five Kage Summit Arc
Shizune was later seen with Naruto, Sakura, and Kakashi, looking down on Tsunade, who was now in a coma. She was later seen explaining to Samui that Tsunade was unable to take the letter meant for the Hokage, and was shocked when Danzō arrived and stated that he was the new Acting Hokage. She is later seen tending to Tsunade and is also present when Sai tells Sakura how Naruto feels for her.

Confining the Jinchūriki Arc
Days later, Shizune senses a heartbeat from Tsunade. She sends one of the shinobi standing guard over them to announce Tsunade's awakening to the Konoha Council and the Fire Daimyō, who was about to appoint Kakashi Hatake as the Sixth Hokage. Shizune is then seen throwing herself on top of her recuperating master, crying out in joy and "squeezing too hard". Shizune was later seen at Tsunade's side when Tsunade was eating a lot of food to regain her chakra. She also panicked when it looked like Tsunade was considering eating Tonton but then realized, with relief, that she was speaking to Kakashi.

Shinobi World War Arc
She was later appointed as the captain of the Logistical Support and Medical Division of the Allied Shinobi Forces. As she introduced herself and Tonton to the division, she explicitly told them that Tonton wasn't to be eaten. She later splits up her division in order to effectively aid all the wounded shinobi on the battlefield.

Naruto Shippūden 4: The Lost Tower
A young Shizune, along with Guy, Asuma, and Kakashi, is seen waiting in a long line at the grand opening of Ramen Ichiraku.

Video Games
Shizune is seen to be able to create swords out of chakra in a move called "Chakra Sword: Great Cross Slash", which causes both physical and internal damage to her opponent, and creates a huge explosion. In many games she is assisted by Tonton in battle; in Naruto: Ultimate Ninja 4, Tonton is used as a partner to Shizune, helping her out in her "Tonton Duo" Jutsu by transforming into an image of Shizune and attacking the enemy to distract them from Shizune's main attack.

Trivia

 * It was shown in a post-credits omake that despite her devotion to Tsunade, she is also wary and insecure about their being single way past the perceived marriageable age, even expressing jealousy to Kurenai Yūhi's perceived relationship with Asuma Sarutobi. Though this was blurted out in a drunken stupor, it did not stop Tsunade from chastising her.

Quotes

 * (To Tsunade) "Tsunade-sama! You shouldn't trust them! Your little brother and my uncle don't wish for that! Their wish... More importantly, your wish... Did you forget them?!"
 * (To Tsunade) " I know what you feel... You're like this now, but you still... Please wake up!"
 * (To Naruto) "You may think you're all healed, you may even look all healed, but you're NOT all healed!"
 * (To Naruto) "All in good time, just as soon as you're completely healed."
 * (To Tsunade) "P-Please wait! I will heal those wounds! Please don't open those seals!"