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The reason Echidna feels somewhat attacked by Icarus words is quite simple. Echidna is the system administrator or rather she is the administrator of the Skarseld's World Voice. Due to this position, whenever the World Voice encounters a problem that it is not able to deal with it. Echidna is the only one responsible for thinking of a solution for it. That's exactly what happened when the Icarus' soul arrived in this world. Where not knowing what it should do with this 'invading' soul, the World Voice had no choice but to consult Echidna, on how it should proceed in this particular case