Her intellect is not very developed. She's just a child. To Reimu and Marisa, she's nothing more than a plain idiot.
She likes playing tricks and often toys with frogs. She freezes them instantly, then watches them revive as they thaw in the water. She tends to fail one out of every 3 attempts, however, and the poor amphibian shatters to pieces.
A fairy who likes pranks. She has the ability to manipulate cold. Without thinking of her own strength, she sets up pranks and ends up having a painful experience every time. That can be said of most fairies, but without reflecting on her past painful experiences at all Cirno sets up pranks one after another. The disaster this time has all of the fairies in an uproar, so she'll probably show up too.
The small fairy was as agitated as usual. Because today, she had seen something bigger than the mountain.
Of course, in reality, it was much smaller than the mountain, but from her impression, there wasn't that big of a difference. It was soon hidden in mist and disappeared from sight, but she was certain. It was definitely the great youkai "Daidarabocchi".
She didn't know where it normally lived, but a moment after she became excited by seeing a rare youkai, the shrine maiden descended from the Youkai Mountain.
"Have you seen any giant robo... anything big moving around here?"
After the events of Strange and Bright Nature Deity, in Fairy Wars, Cirno tries to find those responsible for destroying their house. After learning that it was the Three Mischievous Fairies, goes in search of those responsible, to which defeat easily, because Cirno is The Strongest.
After, Cirno wanders around for a while, bored of weak opponents. While wandering, she encounters Marisa Kirisame, making Cirno think she is a worthy opponent. They battle, and later, Marisa pauses and realising how powerful Cirno was. Marisa goes slightly harder, but is still defeated. Marisa claims that she didn't try as an excuse for her loss.