Satsu's History
Early life and calling
Satsu was born to traditional Japanese parents who wished to see their daughter marry and have children, only to be devastated when she came out as a lesbian. Satsu was activated as a Slayer while in school, and the rush of power knocked her off her feet. Eventually, she joined the Slayer Organization, where she was placed in Buffy Summers' command center squad in Scotland.
Satsu proved to be an exceptional and skillful warrior, quickly earning the respect of her mentor. In turn, she began to have romantic feelings about the older Slayer. When Buffy was put in a mystical sleep by Amy Madison that only a kiss of true love could break, it was Satsu who secretly awakened her, proving that her feelings were far more than just a crush. Shortly afterward, Buffy chose Satsu to come with her to rescue her friend Willow Rosenberg from Amy, battling their way through the U.S. military base with ease. The fact that Satsu was chosen for the mission prompted some friendly envy from her peers Leah and Rowena, who told her not to embarrass them. Satsu was also amongst the troop of Slayers who traveled underground to take down Yamanh of Hoht.
Relationship with Buffy
Some time after their mission to rescue Willow, Buffy once again chose Satsu to help her clean out a vampire nest. Buffy admitted that she knew it was Satsu who kissed her, partially from recognizing the taste of her cinnamon lip gloss. She explained that she was deeply flattered to know she felt this way, but couldn't reciprocate. Buffy warned that people who loved her had a history of getting hurt, a prediction that quickly proved true when Satsu was suddenly knocked out by the masked "Twilight." When she regained consciousness, Buffy comforted her in hospital.
The two Slayers ended up having sex, only to be discovered by Buffy's friends as each walked in on them in bed together. When Satsu commented on Buffy's plan to take all of the Slayers in Scotland to retrieve the stolen MÊ” scythe, Buffy told her to just follow orders, leaving Satsu hurt. This prompted Willow to have a heart to heart with the Slayer, in which she explained that Buffy was different from them due to her responsibilities as leader.
In Japan, Buffy tried to order Satsu to stay behind and offer help to the local Slayers, who had just lost their leader Aiko to a vampire attack. Satsu refused and insisted on taking part in the fight. She participated with Buffy's group during the attack on the vampires' headquarters, taking back the stolen Scythe and plummeting off the side of the building, being caught by Willow moments before landing on the sidewalk. Satsu later commanded the rest of the Slayers, who had their mystical powers taken by Toru's pack, into fighting the rest of the Japanese vampires.
Back at the Slayer Organization Tokyo headquarters, Buffy and Satsu talked about their night together and Satsu's belief she needed to stay away from Buffy, taking the position of leader in the Japan. When Buffy asked if this was goodbye, Satsu offered to leave the goodbye until the next morning, leading them to spend another night together.
Tokyo squad leader
Satsu proved competent in her leadership role. Her squad successfully commandeered a Korean submarine which had been hijacked by vampires. She neglected to report this detail, instead letting her Slayers use the sub to their advantage. Eventually, Kennedy was assigned to evaluate Satsu's position, partially due to her vagueness in the Korean report. Kennedy meanwhile, had a personal agenda, wanting to advise Satsu after her relationship with Buffy. She explained that Satsu was "not the only fool to ever wrinkle the sheets with a straight girl," and advised her to move on from Buffy.
While investigating the Santorio Corporation, Satsu was possessed by a demonic Vampy Cat, which she later nicknamed Fluffy. Kennedy exorcised Fluffy from Satsu's body, and the Tokyo Slayer squad discovered that Santorio Corp were shipping their Vampy Cat inventory to Scotland to attack Buffy. Kennedy and Satsu intervened, and battled the collective Vampy Cats called "the Swell," who revealed their affiliation with Twilight. The Swell was defeated by a missile launched by the Slayers' submarine, and an impressed Kennedy informed Satsu that she would receive a positive evaluation. Afterward, Buffy told Satsu that, in light of vampire Harmony Kendall's reality show making Slayers unpopular with the public, the Slayer army would have to change who they were. Satsu agreed, and disposed of the cinnamon lip gloss she had kissed Buffy with.
Twilight crisis
Satsu was again with Buffy when Slayer Organization members gathered in the new Scotland headquarters, running from direct attacks from the Twilight Group. She sneaked Andrew Wells, his Italy squad, Faith Lehane, and Rupert Giles under the barricade, but the demons following them began to attack the headquarters as well. They escaped to teleported inside a submarine to Daniel Osbourne and Bayarmaa's Tibetan monastery, but they knew hiding was a provisory tactic. Along the other Slayers, Satsu worked in the land to transfer their magic powers into the land, therefore becoming untraceable by Twilight. Being filmed by Andrew, she noted that she felt weak and didn't like it.
Despite their efforts, the group was infiltrated by Amy Madison and Twilight's army went after the Slayers in Tibet. While other Scoobies prepared the depowered Slayers to use military weapons, Satsu led with Andrew a training in which she made it clear to the crowd that people were going to die. After the first battle against Twilight's army, Satsu was present during Buffy's speech in which she told the Slayers that their powers weren't coming back, but their last choice was to collect the injuried from both sides and protect them in the temple.
Satsu then assisted the search for the missing people and the identification of Twilight's headquarters. As the then superpowered Buffy took off, Satsu heard the sonic booms from the fight between Buffy and Twilight. Satsu kept looking for Buffy's location in her tablet while the Scoobies went to rescue the kidnaped Faith, Giles, and Andrew. The encounter between Buffy and Twilight — then revealed to be Angel — made the Slayer's powers to return, including Satsu's. She was able to locate Buffy when she finally stopped moving, but Satsu stormed off and left the device to Dawn Summers when the image revealed Buffy and Angel having sex.
Satsu soon returned, with another tablet, and identified with Dawn the various tears in reality and natural disasters around the world that the creation of the actual Twilight was bringing about. With the Scoobies and other Slayers, Satsu escaped an attack of Placenturians at Twilight's headquarters, embarking Spike's ship to the battle in Sunnydale to protect the Seed of Wonder.
New world
After the Organization's disbanding, Satsu started working for the United States Armed Forces. During world wide attacks by demon lords using the Restless Door to unleash demons on Earth, she was responsible for summoning Buffy to help the army. She gave Buffy the mission to represent humans in the VampCon, in order to reunite classic and new vampires in a same cause.
Although Buffy was resistant to collaborating with the army, who was once the Slayer Organization enemy, Satsu was able to convince her and lead her into a successful mission. She also gathered information from Giles on the Restless Door to help with the army's defenses. At this point, Satsu was also involved with someone.
