Yuyuko (whether she was the Saigyouji Yuyuko or a bodied yukkuri - I'm going for the latter) harbored a strong desire towards the cherry tree - so strong that in death, she haunted the tree in yukkuri form and ironically prevented it from blooming. The group led by Reimu recreated the scene of the tree blossoming, which it reminded Yuyuko of her past and her wish, and as a result she was able to rest in peace, and her desire/curse was lifted, returning the cherry tree to what it used to be.
The question is, who is this Yuyuko, exactly? What was her backstory, and what exactly was the wish that bound her to the tree? Could it have been a desire to see it in bloom, or a reminiscence to her dying moments under the petals that kept her here? Is this supposed to be an alternate story taking its base in PCB's main story?
The largest cherry tree in the forest had been liberated from the strong feelings that had been binding it, and was finally able to return to its original form from decades past, and eternally bloomed beautifully and pridefully.Take it easy!Big sis,I came to play today too!Under This Cherry Blossom Where the Ghost Dreamed
-The End-Welcome Reimu!