When Tokiko was a little girl, the school where she went to kindergarten was attacked by a Homunculus, killing everyone there as they tried to protect her. This incident left Tokiko with a long scar across her face and a deep hatred of the Homunculi. After that day, she began training in the art of Alchemy, and slowly became a formidable force against the Homunculi. She eventually quit her school so that she could become a more proficient warrior. At some point, she joined the Alchemic Regiment, and began to rise through the ranks, eventually becoming a high-ranking member at the age of seventeen.
One night, Tokiko was sent on a mission to eliminate multiple Homunculi in a large Japanese City. After some work and study, she was able to locate a small abandoned factory behind one of the town’s schools in which the Homunculi were coming from. She noticed a large, serpentine Homunculus, created from a teacher at the school in front of the factory, the Ginsei Private School. She followed the Homunculus into the factory, and began posing as an innocent girl who had wandered into the factory in the hopes it would draw out the Homunculus. The plan worked, and the Homunculus attempted to sneak up behind her and eat her before she could run. She prepared to attack, when something suddenly pushed her out of the way, and she turned to see a school boy, around her age, standing where she had just stood. Before she could do anything though, the snake struck forward, hitting the boy directly in the heart, and he screamed with his last breath as he fell to the ground, dead. As the Homunculus prepared another attack, she grabbed the boy’s body and retreated quickly from the area.
Tokiko stopped on top of the school’s water tower, slowly placing the boy on the roof of the water tower. Looking down at the body, she began speaking to him, asking him if he could still hear her. He did not respond, and she told him that this was his fault for being so brash in the face of imminent danger, and that his brashness had lost him his heart to the Homunculus. Then, as she continued to look at the boy, she found her hand going to her right skirt pocket, and her hand closed over a hexagonal object. She continued to speak to stating that he had only thrown himself into danger to save her from being killed, and she pulled from her pocket a Kakugane, an alchemic tool. She bent over with the object in hand, and brought it to the boy’s now heartless chest, telling him that he now was being given a second chance, the power of a new life. The Kakugane slowly began phasing into the boy’s chest, and she told him that he also had a different power, a power only fueled by his will to fight, and that, when he needed it, he would find his Kakugane taking the shape of his weapon. She then lifted the boy up, and using what the boy had on him, she was able to locate his house and his name, Kazuki Muto. She brought Kazuki home, and carefully laid him down to bead before making a swift retreat.
As she stood outside, she began hearing shouting from within the dormitory, and she turned back, hearing the people she deduced to be his friends. She pulled out her cell phone, sending one message to the boy’s cell phone (which she had gotten as she had looked for his address) before turning to leave.
The next day, she began following the boy, who had classes with the Homunculus posing as a school teacher. She realized the danger he was in, as a Homunculus would hunt down someone who had seen their real identity until that person was dead. As Kazuki finished his lunch and the bell for his class rang, he noticed the message on his cell hone, and, as she watched from the water tower that she had brought him back to life, he read Tokiko’s message: “Take good care of your new life.”
That night, Tokiko was called away to some other unknown business, and she abandoned her watch on Kazuki. As she began returning, she had a feeling that he was in danger, and quickly called him on his cell phone. He picked up, and on the other side of the line, she could hear him running away from something, confirming her suspicion. She told him to hang on for the three minutes it would take her to get there, but she was quickly bombarded by many questions from Kazuki about the situation, and she quickly told him that what he was being chased by was a Homunculus, a creature that posed among the humans so that they could get close enough to them to eat them. She then informs Kazuki that she was sent their to kill the Homunculus, and accidentally got Him involved the night before.
On the other side of the line, Tokiko heard Kazuki stumble before he told her that the Homunculus was catching up to him, and she realized that there was no other option then letting him use his Buso Renkin (the weapon created from the Kakugane), and she told him he could now use his powers so that he could combat the monster. Kazuki was shocked at her telling him to fight a giant monster, and Tokiko realized that he couldn’t remember what she had told him while he was dead. On the other line, he said how he was getting out of there, but Tokiko told him just how useless this idea was, as he would be chased by any Homunculus for eternity, and that he could never run away from them. She heard as Kazuki came to a stop, and then he hung up on her. She continued to run back to the school.
When Tokiko finally arrived at the scene, she saw the monster writhing in pain, and she jumped towards it as Kazuki, holding his sister, burst from within the creatures stomach, a lance type Buso Renkin in his hand. As he fell passed her, she commented on how much the lance was like him, as it took no thought to thrust it through a body. She then pulled from her pocket her own Kakugane, and summoned her own Buso Renkin, the Valkyrie Skirt, two leg braces with two arms on each brace. At the end of the arms were scythes, one of which was quickly thrust through the Homunculus’s head, killing it instantly. She then told Kazuki to always aim for the seal on their head, as that was their weakness, before adding that he should be careful how he landed as well, or else he would die.
After the two had landed on the ground safely, Kazuki told her how he had arrived at the factory the previous night. He had seen the Homunculus going inside, and his curiosity had taken the best of him. He followed it inside, where he saw her, who he thought didn’t know the monster was there, and he had died saving her. She told him just how useless that was, as she could easily defend herself, and actually knew that the Homunculus was behind her. The girl who Kazuki had been holding (his sister), who had been propped up on a tree, began to stir, and Kazuki rushed over to her, dropping his lance in the process. Tokiko moved quickly as he stumbled, catching him, telling him to be less rash, as she was in much better shape then him. He said how relieved that made him, and she told him how different he was, adding that that made her at least caused her to like him a little, causing the boy in front of her to blush. She quickly picked up his lance, offering it back to him, and telling him that he had to keep it with him at all times, since it was his new heart. Kazuki then brought the lance in front of him, staring at it, before turning to Tokiko and asking her what Alchemy was. She told him that it was in the dictionary, and she began to explain the complex principles of alchemy to him.