Summary
There are many exceptionally powerful figures in the world ofBleach, but there’s still a very rare ability that enhances power further, which very few Soul Reapers have access to. That ability has to do with their innate Spiritual Pressure, and what makes it different from that of every other Soul Reaper in the Soul Society.
Spiritual Pressure, also known among fans by its Japanese name Reiatsu, is a quality which all spirit beings, be they Soul Reaper, Quincy, or Hollow, exhibit. Spiritual Pressure is the force that one’s Spiritual Power exerts on those around them; skilled Soul Reapers and other such beings are capable of suppressing their Spiritual Pressure, making it more difficult to get a read on their Spiritual Power. Spiritual Pressure is usually depicted as a wave of energy, and particularly strong Spiritual Pressure can render weaker beings completely unable to move.

There also happens to be a special class of Spiritual Pressure which exists, but seems to be extraordinarily rare: elemental Spiritual Pressure.
Yamamoto and Hitsugaya’s Rare Spiritual Pressure is Responsible for Their Power
Elemental Spiritual Pressure Shaped Their Zanpakuto
There are only two characters known to possess elementally-aligned Spiritual Pressure: Head Captain Genryusai Shigekuni Yamamoto, the most experienced Soul Reaper, andthe prodigy, Captain Toshiro Hitsugaya. Yamamoto’s Spiritual Pressure is aligned with the element of fire, while Hitsugaya’s is aligned with the element of ice, as one might expect based on their Zanpakuto. This means that, unlike other Soul Reapers who may have elemental Zanpakuto, Yamamoto and Hitsugaya are able to manifest and control their preferred element even without drawing their swords.
Of course, it’s no coincidence that these two possess elemental Zanpakuto as well; the Zanpakuto’s power and abilities are shaped by the wielder’s Spiritual Pressure, so elementally-aligned Spiritual Pressure would no doubt result in an elementally-aligned Zanpakuto. While there are characters who possess elementally aligned Zanpakuto without having this kind of Spiritual Pressure, likeRukia’s Sode no Shirayuki, their power tends to fail to measure up to that shown by Yamamoto, the strongest Soul Reaper, and Hitsugaya, a prodigy who obtained Bankai long before becoming a captain.

The elemental Spiritual Pressure seems to have been hard to control for inexperienced parties, like Hitsugaya when he was younger; Hitsugaya is said to have released his Spiritual Pressure while he slept, causing the entire house to become freezing cold. Learning to master control of Spiritual Pressure would be even more important than it already is for people with elemental Spiritual Pressure, then, and it’s already considered a critical skill for any Soul Reaper. Yamamoto is said to be able to burn up the Soul Society if he were to fully release his Spiritual Pressure, so control is key.
It’s not clear exactly what makes elemental Spiritual Pressure so rare, or how Yamamoto and Hitsugaya wound up as the only ones with this extraordinary power. It certainly makes Hitsugaya look even more impressive than he already is, while this kind of exceptional power is almost to be expected of a figure as legendarily powerful as Head Captain Yamamoto. Regardless, these two are among the rarest of Soul Reapers inBleach, and this rarity is reflected in the incredible power they each wield.
Bleach
Bleach is a multimedia franchise created by Tite Kubo. The franchise started as a Japanese manga series. Ichigo Kurosaki is the main protagonist who is granted the powers of a being called the Soul Reaper. The success of the manga led to two anime TV shows, four feature-length animations, and several video games.