Question: Is that a fireball? If it is... How is Cirno making one?
Manipulation of ice means manipulation of temperature. If Cirno was as genius as we know and the preservation of energy law works on Gensokyo, that means every time she creates ice the heat would go somewhere, as to create ice you need to create a nuclei to start water crystallization and has correct conditions for it to form. You can't just 'lower' temperature as it would destroy the heat. So in a sense, if she could manipulate ice she also has the ability to manipulate heat!
Manipulation of ice means manipulation of temperature. If Cirno was as genius as we know and the preservation of energy law works on Gensokyo, that means every time she creates ice the heat would go somewhere, as to create ice you need to create a nuclei to start water crystallization and has correct conditions for it to form. You can't just 'lower' temperature as it would destroy the heat. So in a sense, if she could manipulate ice she also has the ability to manipulate heat!
According to Reisen, the heat goes into her own body, so she warms up inside. The main issue is that her ability probably allows her to absorb the heat, but not release it, and taking too much heat would hurt/burn her. That's Reisen's speculation though, we don't really know where the heat goes.
This also makes me think that Rumia's darkness seems to work in a similar way.
This also makes me think that Rumia's darkness seems to work in a similar way.
Absorb light as opposed to simply blocking or reflecting it would probably work better in terms of Rumia. Would also explain why she can't see through her own darkness.