Inner Fire Method

The Inner Fire Method is a training technique invented by Kiyōshi Shinka, in order to help him master the principles of the Fire Release. It involves the circulation of fire chakra throughout his body, allowing him to remain warm even in extremely cold temperatures. He uses this training method by lowering himself completely naked into a tub of very cold water, and then circulating fire chakra to his tenketsu to regulate his body temperature. The colder the water, the harder it is to remain warm. When training to use the Homusubi, Kiyōshi used this technique in water that had a temperature of one degree, which allowed him to gain the chakra control necessary to perfect the Homusubi.

The Inner Fire Method can also be used during combat to temporarily increase the potency of Kiyōshi's fire techniques. However, he must remain stationary and focused when doing so, making him a vulnerable target.