"There is energy all around us. The energy is both yin and yang; positive energy and negative energy. Only a select few firebenders can separate these energies. This creates an imbalance. The energy wants to restore balance and in a moment the positive and negative energy come crashing back together. You provide release and guidance, creating lightning."
Until at least the end of the Hundred Year War, the ability to generate lightning was an incredibly rare skill, usually reserved for the inner circles of Fire Nation royalty and high-ranking military officers. The only firebenders who had demonstrated the ability to actively generate lightning were Princess Azula, Iroh, and Fire Lord Ozai.
Azula demonstrated the technique while training under the watchful eye of Lo and Li and later when she was fighting her brother, Prince Zuko. Some time later, Zuko expressed a desire to learn this ability as well, though his emotional turmoil prevented him from properly creating lightning.
Being a powerful firebender, Ozai was able to generate a powerful lightning strike with great speed, proving not only that lightning can be generated quickly, but also that it can be sustained, or shot in a continuous bolt and held until the user stops producing it. This was seen during the invasion of the Fire Nation on the Day of Black Sun with the Fire Lord's demonstration against Zuko and later the Phoenix King's rapid performances against Avatar Aang during the presence of Sozin's Comet.
Seventy years later, the ability to generate lightning has become more common, though still not widespread. The technique is used in Republic City's power plants, where lines of firebenders generate and direct lightning simultaneously to create electric currents for the city's industrial district. Both Mako and Lightning Bolt Zolt have demonstrated the ability to generate lightning at high speeds.
Generating lightning involves a circular motion with the arms. Mentally, it involves a complete absence of emotion and peace of mind, and physically, it requires separating the energies of yin and yang, also interpreted as positive and negative electric potential respectively. When the yin and yang collide together to become whole again, lightning is created, with the bender only guiding, rather than controlling, the lightning's direction. Because of this complexity, a lightning attack usually takes much longer to initiate than standard fire attacks, though skilled benders, like Ozai, have generated lightning much faster than others less skilled in the art. Mako, however, demonstrated himself to be capable to generate lightning with minimal motion, even while under Amon's bloodbending grip, though it was not lethal. The technique is extremely taxing on a firebender's chi reserves, which is why young men are sought out to work at power plants.
As Lightning Bolt Zolt's short-lived duel against Amon demonstrated, the electric arc produced by this technique can be maintained for several seconds, during which time the lightning can be swept about to produce widespread damage.
Based on the conclusion of the Coup of Ba Sing Se and its aftermath, it appears that if it is not blocked or redirected in some way, a lightning blast will be fatal to any human being, although Amon was shot with lightning and was able to survive. The generation technique cannot be used to defend against lightning; knowledge of a separate technique, lightning redirection, is required.
Zuko and Aang both survived Azula's lightning strikes due to Katara's healing abilities. Aang was fatally wounded, but he was resurrected by the spirit water, and Zuko had to be healed after hurriedly redirecting a lightning bolt Azula fired at Katara. While he was successful in redirecting much of the lightning, his state afterward suggested that Zuko did not have time to finish the move, resulting in some of the energy remaining in his body. This left him incapacitated and unable to keep fighting Azula.
Even in cases where a person survives a strike, it seems they will still be critically wounded: Aang's wound was still raw, to the point where it still bled, and debilitating over a month after he sustained it, and had not completely healed by the end of the War. Zuko's was apparently still raw and painful by the time of his coronation, even though Katara had healed him shortly after he sustained the wound.
The charge, and thus the damage, of a lightning strike can be regulated. During his fight with Amon, Mako was able to control the charge of his lightning, firing a bolt strong enough to incapacitate, but otherwise not harm, his opponent, as Amon quickly recovered from the blast.
- The movements involving lightning generation are drawn from a form of Shaolin martial arts known as "Dragon Shoots Its Whiskers".
- Lightning generation was referred to by Avatar Extras as "lightning bending".