Just as a frame of reference (since I was a bit hazy on the precise dates myself): The last of what's typically considered the "canonical" murders was in early November 1988. The next case to be added to the Whitechapel murder files wasn't until late December of the same year.
Where this puts our sisters... who knows! Perpetrators, aspiring copycats, or perhaps simply fans? Guess we'll find out. Running into Sakuya during all this would make sense, though - I think Miafan's got the right idea.
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The pixiv upload for this comic has slightly different commentary. It doesn't seem like either one is of much consequence to the story itself, but I figured I'd post it here for good measure.
potato pot said: このまえ投稿した話の続きです。またボチボチ更新していきますので、よろしければお付き合いください。
Updated
No..."Jack the Ripper"?The last day of November, 1888How about-We already finished all our work, isn't there anything to talk about?In the mansion in the wealthy west side of town,closest to the poor east side of town.Well then, big sister...Boring.So bored.Nothing to do.The misty capital, London