Celsius (セルシウス Serushiusu?) is the Summon Spirit of Ice. Celsius has appeared in several games of the series as a character or cameo and can be summoned through the Celsius. Celsius is opposed by Efreet, the Summon Spirit of Fire, and she is often seen with her partner wolf, Fenrir. Celsius is named after the Celsius temperature scale. In most appearances, she appears as a blue-skinned woman specializing in martial arts. Celsius is also the only Summon Spirit who has appeared as a playable character in the series.