Shell Bullet is the name of Kazuma's Alter power, which takes the form of armor on his right arm (Stage 1), later extending to the corresponding half of his face (Stage 2), and finally his entire body (Stage 3).
It is unclear when Kazuma discovered the use of his Alter ability, though a brief flashback is shown that indicates the first time he discovers this ability, he had either harmed or killed a person by accident. Later, he is trained by Straight Cougar, being taught how to put his Alter to use, even adopting the "Bullet" techniques that he uses as his own, with the exception the last "Bullet" designation, which is different from Cougar's.
Stage 1: The original manifestation of Kazuma's Alter. It is an alloy-type Alter which transforms his right arm into a weapon. After dematerializing the sufficient quantity of matter (typically the mass stored in a small automobile), Kazuma transmutes it briefly into Alter energy before reforming it into matter enameling his right arm. At its first level, Shell Bullet covers Kazuma's right arm with protective metal armor, which is mostly golden in color but with orange and gray sections. Also, Kazuma's right hand is divided into orange and red plating, with metallic claws for fingernails and 3 red curved fins of metal jutting out from his right shoulder blade that store potential Alter energy, each progressively larger as they near his shoulder (in actuality, it is the middle fin that is the largest one), are created. The fins break apart & release the potential Alter energy that burst outwards to propel Kazuma forward at great speed, increasing the power of his strikes, which Kazuma labels as "Bullets", giving them names that represent their power or affect on the opponent.
◾Fissure Uplift: By punching the ground with, and channeling Alter energy into, the Shell Bullet, Kazuma can generate a small fissure of energy that stretches for about a dozen or so meters, which in turn unleashes a powerful force sufficient to easily launch several victims into the air and away from Kazuma, effectively allowing the break-up of both gang-up and surrounding formations aimed at the user.
- Shōgeki no First Bullet (衝撃 の ファースト ブレト, Shocking First Bullet): The 1st and weakest of the 3 "Bullets" that Kazuma can use in Stage 1. Shattering the most downward Alter power fin (the smallest, which, therefore, is in possession of basic-level Alter power), Kazuma begins to slide across the ground and pivot repeatedly in order to either maintain or increase his momentum, before thrusting his fist at the target and unleashing a powerful wave of force. Kazuma managed to collapse an entire office building by striking its top surface with this Bullet.
- Gekimetsu no Second Bullet (撃滅 の セカンド ブレト, Destructive Second Bullet): The 2nd and intermediate of the "Bullets" that Kazuma can use in this "Alter" stage. Functions the same as "Shocking First Bullet", except that it is the middle/central fin that gets destroyed and the firepower is increased: Kazuma was capable of destroying the large, steel entrance gate to the "Lost Ground" city with this move (likely approaching city block-busting levels, given the quantity of reinforced steel present). "Destructive" is substituted for "Annihilating" in the FUNimation Dub.
- Messatsu no Last Bullet (滅殺 の ラスト ブレト, Obliterating Last Bullet): The third and strongest of the three "Bullets" that Kazuma can use in this "Alter" stage. Functions the same as "Shocking First Bullet" and "Annihilating Second Bullet", except that it is the highest fin that gets destroyed and the firepower is further increased: This is the attack that ranks Kazuma at multi city block-busting power, capable of wiping out hundreds of thousands of cubic meters worth of rock in energy collisions with equally-powerful "Alter" users. "Obliterating" is substituted for "Exterminating" in the FUNimation Dub.
Stage 2: Stage Bullet Ultimate: The first evolution of Kazuma's Alter, attained after the Shell Bullet interacted with Alter parallel dimension-native material (namely, a piece of "The Crystal" Alter's rib-cage). After matter is de-materialized and reformed onto Kazuma's right arm, it now takes the appearance of a predominantly-orange plating that now extends across half of the limb's length before segmenting in half. The armor is thicker and is later revealed to replace his entire arm instead of simply covering it. For some reason, whenever summoned, it possesses a small, grey or silver brace on its wrist that falls off when used, possibly serving as a sort of temporary lock until he decides to use his arm; in that case, it disengages from his arm by way of destruction via the arm opening for use. 4 orange fins appear/extend around the corresponding side of Kazuma's face (towards his right eye), and a large, golden propeller is located where the 3 red fins used to be. This propeller grants Kazuma flight, as well as eliminating the firing limit imposed by Stage 1. On his fist is a small aperture which can absorb additional Alter power, further strengthening his attacks, which he calls Shell Bullets. Also, this stage of Shell Bullet is the only one that demonstrates regenerative properties, as it was once damaged and severed from Kazuma's body and then reattached itself to him by de-materializing and reforming back into its place.
◾Shell Bullet: Uses the propeller on his back to propel himself forward while gathering alter energy from the duct on his arm, this was the technique he used when he caused the second upheaval of the grounds with Ryuho.
◾Energy Absorption: The aperture duct embedded into Kazuma's right hand is capable of absorbing atmospheric traces of "Alter" energy in the local environment and redirecting it into his personal reserves. This is the primary method of Shell Bullet Ultimate, with Kazuma gaining the energy needed for his special attacks.
◾Shell Bullet Burst: Kazuma channels all of his collected Alter energy into his aperture, causing a blinding golden light to emit from his right hand, before throwing a punch at a target. The resulting strike releases all of the energy in one blast, extending well beyond Kazuma's mêlée range (effective to at least dozens of meters) and retaining the golden luminance in the shape of a fist. Capable of immediately disintegrating the structure of Biff's Hammer Alter after its refinement.
-Before charging up the propeller, he uses his duct to gather energy. While in this process, he has a habit of announcing "More power... AND MORE!! AND MOREE!!!! SHINE BRIGHTER!!!!!!!!!!", often roaring the last verse.
Stage 3: Proud Fist: In his final form, achieved from pushing himself and his ability beyond his natural limits with his resolve to defeat Kyoji Mujo and avenge all of his fallen comrades at the hands of the mainland Alter user, Kazuma's Alter, which previously extended only the length of his right arm and individual pieces on his right shoulder region, now traverses across his entire form as a type of "bodysuit", streamlined to his body and sharing the same color scheme as his right arm. The four-fin face-pieces have now fused and extended across to form a mask, while a large wave of jagged, red "hair" juts upwards from the mask, causing him to appear as a humanoid cross between a samurai and a lion. His Alter energy-absorbing arm grows even larger than his second form and, in addition, his left arm becomes armored and possesses an aperture duct, and his propeller is replaced by a long, flexible, tail-like appendage which acts like a whip, serving much the same purpose as the fins from the first form or the propeller in the second form did (no longer requiring the latter with freeform flight), acting in the same manner as an anti-gravitational propulsion unit used to push himself wherever he wished to soar at high speeds. In addition to this appendage, a secondary, smaller one appears on the back of his left side (which could indicate that his final form could become much stronger over time, as the smaller appendage may grow to the size of the whip on his right side). After using this power, Kazuma has several connecting scars on his arm that originally held his Alter power at Stage 1.
◾Dimensional B.F.R. (Big Fat Rift): With his humungous boost in raw power, Kazuma can distort the fabric of space with his punches and voluntarily tear open a rift to the Alter dimension parallel to the real world. From there, he can throw opponents inside to banish them to it; once his desired victim is inside, the rift closes and seals them within, trapping them in the Alter dimension permanently, and only fellow Alter users that attain a similar evolution to Kazuma or Ryuho (the mutated Kyoji Mujo) are capable of escaping from the parallel realm. The tear can extend for up to several kilometers in horizontal length (left to right, vice versa), allowing the banishment of more beings in a short space of time.
◾Giant Explosion Fist: Proud Fist Kazuma can also generate incredible, raw firepower from his standard punches, with individual strikes ranging from over 100 to several 100 kilometers in width and are capable of breaching past Earth's orbit when concentrated into beam form, or expanding across a large portion of the planet's surface (easily viewable from outer space).
Stage 1: An augmentation-style Alter manifestation. While typically used by Manga Kazuma as an immense boost in physical attributes, especially physical strength, and range-of-effect with his punches like his anime counterpart, Shell Bullet in the manga also has some more exotic properties: it appears to possess a natural adaptability system which enables it to interact with concepts such as souls of the deceased, other Alter manifestations and even its own shape in order to maximize its effectiveness potential in battle. The characteristic three fins, which represent the limitation of full-power punches Kazuma can perform in the anime, notably do not shatter upon using a full-power punch, meaning that Manga Kazuma has effectively unlimited usage with Shell Bullet.
◾Empathetic Empowerment: Manga Kazuma does not use Shell Bullet at full-power by tapping into dormant reserves within the Alter itself (as within the fins in the anime), but rather by experiencing powerful emotions and using such personal conviction to augment incoming blows. This is usually expressed by Kazuma shouting "Shell Bullet of -!!!" with the - depending on the exact type of emotion he is feeling (i.e, anger = Rage; remorse = Grief).
◾Soul Absorption: Manga Kazuma has the ability to temporarily assimilate the spirits of deceased individuals into his "Alter", storing them in what appear to be small capsule-like rods on Shell Bullet, that are discarded once the spirit departs Kazuma. The spirits appear to be capable of enhancing Kazuma's physical stats, but their most dangerous application is the transfer of their knowledge and memories from Kazuma to an opponent via physical contact, forcing the target to experience the life of a victim they murdered or harmed in visions. The aftermath of such events often lead to complete mental breakdown.
◾Ability Replication: Another ability of Manga Kazuma is the trait of his Shell Bullet to temporarily absorb the attributes of another "Alter" through unknown means. This is only seen in effect against Cougar's speed Alter: the first time to avoid an incoming Cougar Speed attack. The second occurance is debatable, and if true would indicate that the ability-replication effects are infact long-term: Kazuma appears to boost himself in the air to reach HOLY's headquarters with Cougar's speed.
◾Body Alteration: Shell Bullet is shown to be highly versatile even in the arrangement of its physique: Kazuma demonstrates this by arranging the structure of the arm into a mirror, in order to reflect the magnified light generated by Aono's "Shield of Distortion".
◾Healing Acceleration: Presumably through his ability to deconstruct matter, Manga Kazuma demonstrates the power to forcibly permeate medicine through his skin and directly into his bloodstream, massively accelerate his healing factor rate and recovering from injuries in minutes, what would normally take days or weeks to naturally heal. Forms prominent spikes around his body wounds in the process.
Death Bullet/Shell Bullet Stage 2: The evolution of Shell Bullet following Kazuma's experience of the S-CRY-ed world. A full-body augmentation-style Alter transformation. Presumably retains all the abilities demonstrated by the previous Shell Bullet form, plus with massively increased physical attributes and a single, highly potent effect addition.
◾Effect Reversal: A highly potent ability of Death Bullet Kazuma is his power to "reverse" the position or nature of any physical or energy-based ability with physical contact. First seen when he reversed the lens of Aono's "Shield of Distortion" so that the magnification process minimized from Aono's position and maximized on Kazuma's.
◾Fist of Pride: Manga Kazuma's ultimate punch and used to kill Galan Du. The force of this punch was sufficient to fire its effect as a beam of energy escaping into outer space and still form a crater 100s of meters wide on the ground.
◾Mental Treason: A powerful skill, described by Cougar Straight as the ability to "think weak" and to forcibly suppress those detrimental thoughts to ensure that Kazuma will enter combat with full confidence in his own capabilities. This is the origin of Kazuma's moniker "Treasoner" and the reason why he will never consider fleeing from a battle; he was even capable of continuing to fight after experiencing a death premonition from Aono that completely paralyzed a veteran Alter user and fighter, Akira Mijyo, in her tracks.