Board Thread:Theories Discussion/@comment-25886565-20150812203149/@comment-6192846-20150813015700

It's a curiosity mothy will have to tackle at some point. Irina claims, as Maxus pointed out, that Irina felt Elluka was taking Kiril away by making him "different" from her by removing his syndrome. The narration of Lunacy claims that her wails and regret over her first kill (Elluka) was an "embarrassing past" from when she thought she was a "normal human".

The middle ground based on those two points was that Irina was jealous of Elluka getting close to Kiril, curing his HER Syndrome, and getting all his attention while not being aware she herself was specifically a HER, only learning sometime after her murder (Seth being the likely source). Perhaps she was even in denial herself, hence "hiding" it from Elluka.

The issue there is still why Elluka wasn't able to detect it if she should've been able to tell Prim was one. It's possible Elluka simply put her faith in Kiril, who we know was completely certain his sister couldn't be a HER based on her outward behavior.

Unless we know Elluka's method, however, it's difficult to deduce the motivations. I mean, this ability seems unique to Elluka thus far. Worst case scenario, Irina was mistaken in believing her sister-in-law actually could cure HERs of their condition and was merely using some technique to suppress it or temporarily subdue the symptoms. I find that unlikely, given the circumstances.