This I think qualifies for that bizarro tag since light is the opposite of dark and Rumia canonically manipulates dark which alters her ability in this which she manipulates light (sunlight).
Theoretically, she can pull this off. She can control and manipulate the darkness - so by causing it to go away, she gets the same basic effect. The sphere of darkness can become a sphere of light if she simply rejects all darkness near her - essentially causing there to be naught but light left. [/nerd]
ZUN said: A youkai that can control light - doesn't that sound really powerful?
Nobody knows what he was implying, but it seems that she can't control light (yet?). If Rumia's 'manipulation' is limited to creating darkness, for instance.