|First Appearance||Chapter 89 |
|Last Appearance||Chapter 182 |
|Voiced by||Sanae Kobayashi|
|Known Relatives||Fumio Honjou|
Setsuna was the daughter of the master mathematician Fumio Honjou. Her mother passed away while she was at an early age. She was a university student who had a serious mental disease which caused her to become uncontrollably mad at certain periods during the day. Because of this, she was put under the supervision of Eisuke Harukawa, who was a famous neurologist.
Harukawa described Setsuna as being a gentle, brilliant intellect who was very easy to communicate with. He eventually grew attracted to her and was devoted to heal her of her mental disease. Setsuna liked cicadas, as they were insects that kept their own "personalities", going through years as larvae underground and emerging as their winged-adult form.
Setsuna's name is equivalent to the Japanese pronunciation of the numeral 1/100000000000000000, and was the final password that guarded HAL.
As Fumio Honjou later reveals to Yako, Setsuna wasn't born with a mental disease, and it wasn't a mental disease which killed her. While she was still a university student, Sicks had come to seek her father's assistance. After observing X's inability to maintain her memory, Sicks had created a medicine which would strengthen the brain a hundredfold. However, the medicine was so powerful that it would destroy the brain of anyone whose brain wasn't already strong and in constant use. Originally, Sicks had planned to use the medicine and experiment on Fumio, who being a genius, had a chance of surviving the medicine's effects. His plans changed after he saw that Setsuna too, was quite intelligent. Sicks asked Fumio to allow him to experiment on Setsuna, even though there would probably be a greater chance of failure, because he wished to see one of his favorite expressions: that of a parent giving up their child to him. Fumio agreed, and Setsuna became Sick's guinea pig until her brain couldn't handle it, resulting in her 'mental disease'.
At some point, Setsuna was admitted under Harukawa's care for her mental problems. Harukawa grew attracted to her and did all he could to heal her. The disease grew worse everyday however and her mad personality eventually took over her normal personality. Harukawa was heartbroken, and when she finally died, he swore to recreate her in both looks and personality with just his knowledge and memories of her, a goal which would eventually lead to the happenings in the HAL arc.
After Neuro and Yako beat HAL, HAL explained his goal and Harukawa's past with Setsuna to Yako. After Yako deleted HAL, he sees a vision of Setsuna at the final moment and expresses his satisfication.