It's real convenient that Mari sells this in her shop. And as long as no one witnesses it, it'll be very clean too, with a nondescript rope and a Narby nearby.

Spoilersis who want to see the bad ending. If you already completed the chapter with complete 10/10 memories, follow this steps:
>go to day 9, 22.00 Late night
>there will be a checkmark "reset all memories", do it
>finish day 9 until the end
>go to day 14, 5:00 Dawn
>watch the cutscene