Twilight is a smart girl, often looking towards pure logic, and will try her best to study things that can't be easily explained. When something abnormal presents itself, she either becomes completely freaked, or very fascinated, which shifts completely depending on what she comes across. She can be sweet, but, tried to keep things neat and scheduled as much as she could.
During her childhood, she attended a girls-only club, where she first met Nagisa. As time went by, she grew attached to Nagisa until her parents decided to move away.
After seven years, she and her family moved back to Tokyo, where she was soon reunited with Nagisa back at the high school. She told Nagisa how much she missed her, she had to cut it short when the bell rang, having to go to class. Later on, she met up with Nagisa at lunch time, and was told about Korosensei. She didn't believe him, until he showed up himself, Twilight passing out from pure shock.
Sometime later, Twilight decided to go to Nagisa's campus to study Korosensei, to see how he worked, when she came across Nagisa again, and asked for his help. She and Nagisa went to study Korosensei, but only got down how quickly he could move before she was caught. Soon, she also came across Greninja after the failed study, and was warned about Giratina's monsters. She returned to the main building, distracted by the thoughts until Akari Yukimura got her attention again, and she went back to her work.
Eventually, Twilight saw Nagisa with Karma Akabane, and tried to convince Nagisa to not go with him. In the end though, Twilight had to let him go off with him, though remained worried until Nagisa had returned. Sometime after, Twilight and Akari took one night for a late study, when Twilight was suddenly found by Misao, which made her trapped inside until Nagisa showed up and saved her. Twilight then helped him with releasing Misao from the school.
Sometime later, Twilight met back up with Nagisa when she found Korosensei sickly. After some convincing, Twilight decided to create a substitute teacher, Ritsu, for Korosensei while Twilight kept Korosensei back at her house in order to take care of him. Korosensei became better, and Twilight continued on her life until she went back to Class 3-E, finding Luffy and Naruto spying on Karma, Ren, and Nagisa. Twilight grew curious as well, and decided to follow them, soon finding out about their involvement thanks to Greninja. Afterwards, Twilight found out that she possessed the Multitype Seishin-Tekina, the power of magic.