Ice fairy Cirno is a character from the Touhou Project (Project Shrine Maiden) game series. She first appears as boss of the second stage in Embodiment of Scarlet Devil, sixth game in the series and the first one to be released for Windows OS. As a second stage's boss she isn't a big challenge, but she is incomparably stronger than other fairies, who are the weakest kind of enemy that player may encounter.
She is a mischievous character with a very strong personality. Her big ambition and self-confidence drive her to challenge characters that are out of her league, what could be the reason why she was labeled as an idiot in Phantasmagoria of Flower View, ninth game of the series. Latter facts refer to Touhou memes about Cirno being an idiot (also known as because of the game's manual design) and "the strongest".
Based on dialogues in Phantasmagoria of Flower View she is said to be over sixty year old. Even though most sources call her a child in terms of her kind, it's not a proper way of thinking, since fairies in the Touhou universe are immortal embodiments of natural phenomena, with their bodies regenerating very fast. Due to author's trivia they also regenerate right after "death". Her appearance is one of a female human child with icicle-wings, light-blue hair and blue eyes. She wears a blue dress with a white pattern on the lower part and a blue ribbon (in some games she appears with a green one, though). She usually, but not always, appears with white socks. Blouse she wears under her dress was originally light pink, but it was changed to white in Fairy Wars.
Her name comes from japanese pronounciation of english word "chill" (chiru), after adding the japanese "no" we basically get "of the chill". It's said that getting rid of the "h" was meant to make the name look a bit italian, what could be true, since there is an italian name Ciro with diminutive version Cirino. Other theory mentions cloud type Cirrus, which produces falling ice crystals.
Despite being one of the most popular characters in the game series, and one of very few that are playable in the singleplayer danmaku parts, her role in author's official comics is very small, even when she is the player character in the game directly related to story presented in the manga.
(Source: official manga, game and author's trivia)
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