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, and she is implied to be so in Phantasmagoria of Flower View by Eiki Shiki. Her personality is childish and rather incompetent, as you might expect from her appearance.