Mmkay, the explanation is that when you bury the yukkuri within a high-nutrient soil, then let them grow, the stalk that grows from their butt is literally a clone.
So that Marisa that grew from the planted one is basically a clone of the dead Marisa.
However, as if hearing nothing, miss continues to kick Reimu with her knee.
With every kick from her knee, Reimu's body becomes more and more twisted.
In the midst of miss' continued kicks and Reimu's scream, something mysterious is happening.