Isuka's sister and former partner who were both created and raised by the Alchemists before Ikaruga's departure. The two were thought to be inseparable during their youth and considered one of the greater assets to the Alchemists. Both viewed each other as halves of a pair but their peaceful days of experimentation and engineering came to an end with Ikaruga being influenced to see the outside and break away from their perpetual peace. Isuka from both the start of Ikaruga's change and after started to fear for her sister's active effort in differentiating herself and attempted to change her mind at every turn. With her formal leave, Isuka understandably felt abandoned and as punishment, a chip that inhibited complex emotions was installed on her brain to ensure that she would not break away from the Alchemists and further fueled her ire towards Ikaruga for leaving her behind and letting her be punished for a mistake she was not a part of.
However, Isuka's love for Ikaruga ultimately exceeded her passion to invent and design and this was revealed at how Isuka had actually wanted to leave with Ikaruga was unable to follow through with her emotions. This revelation however came too late but Isuka was able to die in Ikaruga's arms and forgive her.
The elf-child created by Ikaruga in a intentionally botched experiment to have herself evicted. The basis of Kanaria's creation was to produce a magic adept dark-elf but Ikaruga altered the experiment to instead create a wood-elf that boasted high physical attributes while having no inherent talent with magic. Kanaria's creation was one of the reasons Ikaruga was motivated to leave and Isuka initially did not want anything to do with Kanaria, who was also left behind but thought dead by Ikaruga. Isuka avoided contact with Isuka as the "reeducation" process caused her pain if she felt strong emotions and Kanaria's presence itself reminded her of Ikaruga. But while Isuka rejected Kanaria, she wasn't completely unable to distance herself and soon came to view Kanaria as a replacement for Ikaruga's absence during Isuka's rare fits of emotion. Isuka came under suspicion from the Alchemist's higher ups and Isuka gave Kanaria refuge with Valhalla and hoped for Kanaria to live without pain and suffering and truly be free, unlike the caged birds that every Suginami was.
A necromancer affiliated with Valhalla who approached becomes affiliated with Isuka where the two came to an agreement that if Isuka was successful in resurrecting the dark-elves, she would be able join Valhalla's ranks. Isuka's own desire to break free from the Alchemists had her willingly agree to assist Valhalla if it meant pursuing her own research interests and in exchange, Haunted utilized the 5th Laboratory as his hideout after slaughtering every alchemist inside per Isuka's request. Isuka didn't pay too much mind to Haunted and toiled about her research while the latter particularly didn't like the way Isuka thought about killing others and the fact that she felt so little to begin with. However, the two seemed to have some degree of respect for each other as both were scientifically gifted. But in the end, whatever fondness Haunted had toward her was expressed in his most sincere gift of killing her upon the first sign of intense emotion, something he had craved to see in her.
Isuka had no personal grudge against Ikaruga's platoon members but viewed their opinions on Ikaruga to be completely naive as they had no idea what kind of person she was before they met her. Isuka quickly removed them as per Ikaruga's request that they were kept safe.