Cirno

Cirno is an ice fairy. While she is described as a weak boss in the Touhou series, if we consider the power of average fairies - who appear often as regular enemies - we can certainly say she is exceptionally strong for her kind. Her personality is childish, as you might expect from her appearance, and she is sometimes considered stupid.

During the events of Embodiment of Scarlet Devil, she attacked the player, who was just passing by, out of instinctive aggression. She was helplessly shot down.

In Perfect Cherry Blossom, she returned to take revenge for her previous fight, but was only a mid-boss and was easily defeated like one.

In Phantasmagoria of Flower View, Cirno aimlessly wandered about, apparently unconcerned by the flower incident for any reason other than the flowers being something else for her to freeze and play with. Through her dialog, her true childish nature is revealed, leaving no doubt that she really isn't smart at all. She really wasn't meaning to do anything but play games.

In Touhou Hisoutensoku, Cirno was intrigued by what she believed to be the great Daidarabotchi and hoped to tame it so that she won't be afraid of anything anymore. She showed more intelligence than in the previous game, as she has lost her habit of starting fights and admitted that she is incapable of defeating the Daidarabotchi if it lives in the hot spring's boiler, since it is too hot for her.

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.

Appearence
(Touhou 9, 12.3) Same as above, except her ribbon is green instead of blue (however her sprite in 9 still keeps the blue ribbon). (Touhou 9, alternative outfit) Same as above, except her bow is a darker shade of green, her blouse appears light purple, and her dress is purple as well. (Touhou 12.8) Cirno's bow is once again blue. Her blouse has been changed to white. Has bigger eyebrows.
 * (Touhou 6,7) Aqua-colored eyes, hair and icicle-shaped wings. Wears a blue ribbon, light pink blouse and blue jumper dress.