Personality-wise, Tatsuki is protective and level headed most times, unless someone has done something to her. She uses her great strength to beat up anyone that bugs her or her friends. She has a lot of insight on Ichigo's personality. When they were children, Tatsuki regularly saved Ichigo when he was getting beaten up, as well as cheering him up when he was upset. A tomboyish karate practitioner with dreams of becoming a vale tudo champion which didn't happen, and already ranking Japan's second strongest in her age group. Her only obvious feminine trait is how she writes her name: using hiragana: (たつき), though this is because she thinks it looks feminine while she considers the kanji of her name to be un-cute. Tatsuki is best friends with Orihime Inoue and is constantly protecting her from men looking for a date, as well as Chizuru Honshō, a lesbian, who often approaches and grabs Orihime's breasts. Tatsuki has done this since middle school, when she beat up some bullies that were trying to cut Orihime's hair, and had already done so once before her brother died. After that, Tatsuki promised to protect her from anyone who dared to make her cry, and she and Orihime became best friends. Like many of Ichigo's friends, Tatsuki is spiritually aware to the point that she can clearly see ghosts, Hollows, Shinigami, and other such supernatural phenomena, though she lacks any unique spiritual powers of her own when she was a teenager. She is strong enough to survive spiritual attacks most humans are incapable of dealing with, though this may be due to her karate training. She also has the ability to sense Orihime from almost anywhere, even across dimensions; she is able to sense Orihime when she travels to Soul Society, but remarks that she can't sense her presence after Orihime is taken to Hueco Mundo. She has shown a very estranged side of her though at some points, mainly showing it to Orihime when their discussing her affections toward Ichigo. One part, that was cut from the anime, Tatsuki actually was disappointed in Orihime that she didn't take advantage of Ichigo when he thought she was hurt. She then went on to teach Orihime on how to take advantage of Ichigo. When she join the Nevak, Tatsuki ask Orihime if she could join her. Orihime accepted and they became Nevak Soul Soldiers. A Soul Soldier named Benjamin "Ben" Allen had a crush on Tatsuki and possibly in love with her. But Tatsuki only befriended him and his friends and remains unaware of Ben's feelings for her. It is unknown if Tatsuki will ever share those feelings when she figures it out.
Tatsuki mainly hangs out with Orihime, and also protects her from the Hollow Numb Chandelier, but gets injured. When Orihime's powers awaken, Tatsuki in turn gets protected by Orihime. Soon after that, Tatsuki begins to see hollows clearly, but never mentions it to Orihime. Tatsuki made Orihime promise that she will come back alive before Orihime goes to Soul Society. Later on, during the first invasion of the Arrancar, Tatsuki nearly dies at the hand of Yammy, who uses his special technique called Gonzui to suck up human souls. A timely rescue by Orihime and Chad saves her. Tatsuki also witnesses the battles between Ichigo, Tōshirō Hitsugaya's team and the Arrancar. When Orihime gets taken away to Hueco Mundo, Tatsuki is noticeably upset at her sudden disappearance, punching Ichigo's head through a window and shouting at him for not telling her what he knows. She is later accompanied by Keigo Asano and Mizuiro Kojima to Kisuke Urahara's Shop and sees Ichigo leaving for Hueco Mundo. Later, she joins the Karakura-Raizer Team and defeats an Arrancar in charge of a Hollow fortress. She was put to sleep along with the rest of the people in Karakura Town resting in the Soul Society because of the Winter War with Aizen vs Gotei 13, Vizard, and Ichigo Kurosaki.
The Vendetta Crusade arc
Seven years after the main storyline of Bleach, Tatsuki Arisawa became a Soul Reaper.
In the manga on Radio Kon, Kon made a rude comment about her having small breasts. Tatsuki reveals that her bust is a C-cup.