Spark

Spark (種火, tanebi) is an emitter quirk used by Shojirou Atsuki.

Description
Shoji creates small amounts of metal through the pores of his skin, which are then heated to very high temperatures to give off tiny molten sparks. This quirk can only be activated when he comes into physical contact with a surface or object, and can activate his quirk on any part of his body, but prefers to use it with his hands.

With a snap of his fingers, sparks fly. Shoji's sparks are usually a generic orange colour like fireworks, and the strength of the spark cannot always be controlled, allowing some sparks to be bigger than others. The colour of the sparks can vary, depending upon the emotion that he is feeling, easily acting as an indicator for his true feelings. Shoji’s quirk allows for him to have not only innate heat resistance, but also to be able to warm up his body at will to combat cold temperatures. Shoji cannot heat his body when faced with extreme cold, and his quirk becomes useless at temperatures around or below -50°C. His ability to heat his own body leads to him being treated as a human heater during winter by his family, as they wish to save on their electricity bill.
 * White indicates sincerity or pity.
 * Black indicates violent eagerness and malicious intent.
 * Red indicates anger and fury.
 * Green indicates envy and jealousy.
 * Purple indicates unease and stress.
 * Blue indicates calm, or a sense of contentment.
 * Yellow sparks fly when Shoji is excited.
 * Pink sparks indicate surprise or bewilderment.
 * Brown indicates Shojirou is fed up, annoyed, or has generally had enough of something.
 * Orange indicates confidence, pride, and fulfilment.
 * Turquoise sparks indicate Shoji is confused.

Despite having heat resistance, Shoji cannot create sparks with his quirk for more than ten seconds, as it will begin to melt his hand due to the high heat generated. Although the heat that generates the sparks can also melt other types of metals, once it reaches the ten second limit of his quirk, Shoji cannot generate sparks for a minute or two until his skin cools off. Not only this, but Shoji's entire body circulates heat around, and thus overuse of his quirk leaves him dehydrated and sluggish, potentially leaving him with heatstroke despite environmental conditions.

His quirk, Spark, is actually a "defective quirk" born from his mother’s quirk of fire and his father’s quirk of metal. The defect lies in the fact that although he inherited both of their quirks, they activate at exactly the same time - something which he cannot control. Originally, he was unable to control where he could manifest this quirk either, and only after both psychological and physiological quirk therapy was he able to control where it is manifested on his body. The buildup of the metal Shoji uses to create sparks happens naturally, and they accumulate underneath his skin. This results in Shoji constantly having a metal layer underneath his dermis, and becoming susceptible to electrical and magnetic attacks.

Usage
Despite it's classification and Shoji's referral to Spark being a defective quirk, Spark remains very useful in specific situations. By itself, it passively warms Shoji, making him much more resistant to the cold, and capable of squaring off against cold-based quirks with little harm so long as he is not frozen to a temperature below -50°C.

Shoji's quirk is also useful in conjunction with other quirks, particularly Cinder. Spark is capable of easily setting alight any materials that are naturally flammable, such as wood or paper, and Aoki is careful to avoid the action of Spark as it can easily set him on fire.