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No.180
This will be long winded.
First of all, Poniko is the embodiment of Madotsuki's happiness, at least the happiness she used to have. It's most apparent from the balloons and the bright color theme of the room she's in, plus the similarities between the looks of both her and Madotsuki.
Now, when you murder Poniko (YES YES I KNOW YOU DO NOT HAVE TO KILL HER TO GET UBOA) then it's a representation of the end of happiness. Turning off the lights brings in the darkness and causes misery to take form, in this case it's Uboa. Trying to escape Uboa is impossible, as you can never turn back from what you've done in the past
Uboa is nothing more than the manifestation of the depression and pain that Madotsuki has felt over her lifetime, probably from something that happened in her past. Because of this, when you touch Uboa, embracing misery, you end up in a world you cannot escape, doomed to walk in nothing forever (least until you pinch your cheek).