Ah. It's a wonder no-one had thought of this before.
<PCB: Youmu explains that she had been stealing the essence of "spring" throughout Gensokyo in order to make the Saigyou Ayakashi, a youkai cherry tree, bloom perfectly with the rest of Hakugyokurou's gardens, as per her master's orders.>
<Yuuka Kazami: Abilities: Manipulation of flowers, for example to make a flower tree bloom.>