Translation of Spoiler from internet
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Finished reading Accel World 23, regarding the life of Kuroyukihime: (Important spoiler please be caution)

She's a manchine child who was born out of man-made uterus, installed with Neurolinker when she was still in the man-made uterus and her parents used STL to overwrite her original soul, and also  resulted in a barcode left on the back of her neck.

Initially at the time there were two companies who have acquired the technology of STL. One of them is RECT who's widely known from the SAO incident, another is カムラ(KAMURA). Notably, the original family name of KYH's mother was 神邑, also pronounced as Kamura, and she's from the company that created the company. KYH's father was also a researcher from Kamura.

Which mean although genetically KYH is indeed children of their parents but they aren't related in term of soul.

KYH estimated that her soul was probably from another new-born baby since the brain of a new-born baby would not be able to support the soul of an adult (She used an example of stillborn baby here as one of the theorized source of her soul)

KYH think her parents still haven't know that she have gathered this much facts, as all of them were found out by themselves after Graphite give her the SSS Order and she hacked the Kamura headquarter's server to fins out all these information, however there are still many details about the soul copying experiments remain unclear, no matter it's about the ultimate objective of the experiment or the source of her soul, when KYH asked her elder sister about all these she simply answered that the barcode would disappear after grown-up.

Written on the barcode is a series of digit "20320930" which is KYH's birth date. According to record, she stayed in the man-made uterus for 13 months and thus she guess there're some special reasons behind why her parents picked the date for her to born.