[Marina2]

I went around internet to find some additional explanation how Izayoi arrived at the solution of the false legend. I found some good explanations from Randomc ,so I will share them here.

Spoiler for explanation about Fake legend & Shiroyasha seal:

Originally Posted by daikama

zayoi points out that the myth/story/whatever is that on ONE day (June 26, 1284) 130 individuals “disappeared” from the town of Hamelin. In otherwords, the cause of their “disappearance” (which could also be taken as death), must be something that kills within 24 hours. The Black Plague aka Black Death or Great Pestilence is thought to be caused by Yersinia Pestis bacterial infection. Death occurs several days after symptoms first show. In short, the Black Death did not kill people in 24 hours or less. Therefore it doesn’t fit within the Hamelin myth.

As for Shiroyasha. About the same time as the Black Plague/Death began (approx. 1347), Europe along with N America and other parts of the world began to experience what’s informally referred to as the “Little Ice Age.” (NOTE – dates for this period are widely contested). It wasn’t a true Ice Age in scientific terms, but there was a significant decrease in average temperatures along with longer, harsher winters, shorter & cooler summers, etc. Figuratively speaking, during an Ice Age, it could be said that it’s as if the sun (representing warmth) is “hidden” or “restricted”.

My impression is that Izayoi realizes the (theoretically) simultaneous timing of the two events – the Black Plague/Death & Little Ice Age. From that coincidence, he then concludes that Pest is not only the embodiment of the Black Death, but also represent the “(Little) Ice Age” as well. Thus she has the power to “restrict/conceal/capture” (however you want to phrase it) “the sun”, or in this case, Shiroyasho who represents the sun in little garden.

Spoiler for Explanation for Why break the glass with "Jocker controlling rats" and keep the one that doesn't have rats in it:

Originally Posted by jrj

..it is exactly how Izayoi was able to know which legend are true and therefore to protect, and which ones are false and therefore to smash… Because rats are another symbol for Pest (due to how the disease can be carried by rats), any color glass that has rats on it is associate with the pest version of pied piper (which is false). Since only pest was slow death, pest could not have been the true legend (plus time period does not match… the true events happened in 13th century, yet black death occurred after 14th century)