The Bane Bane no Mi is a Paramecia-type Devil Fruit that allows the user to turn their limbs into springs, making the user a Spring Human (バネ人間,Bane Ningen?). "Bane" means spring. It is called the Boing-Boing Fruit in the Viz Manga and the Spring-Spring Fruit in the FUNimation dub. It was eaten by Bellamy.
The power of the fruit was hinted at with the state of the site where Roshio was defeated. The fruit's actual power was revealed when Bellamy and his crew attacked the leaders of the Saruyama Alliance in order to steal Montblanc Cricket's gold.
The major strength of the fruit is that it gives its user the ability to transform parts of his body into springs. By applying this to the legs, it grants the user amazing jumping and bouncing power, which can be used to launch himself at incredible speeds, in order to deliver attacks enhanced by a high magnitude of momentum.
Due to the reactive force of bouncing off a solid surface, the user can break apart the said surface, as the Going Merry was split in half as a result. By applying this ability to other portions of the body, such as the arms, it can release strong, longer-ranged punches. The user can also turn his abdomen into a spring, which grants him more flexibility.
The weakness of this fruit's powers lies within the self-propulsion by turning the legs into springs: the user can only be propelled in a straight direction, making it easy for the opponents to predict the trajectory and counterattack. Furthermore, the user needs something solid to bounce off of, thus the direction is based on the geography of the battlefield. However, such weaknesses do not apply when the power is used to launch a spring-loaded punch or kick. Other than that, the fruit has the standard Devil Fruit weakness.
The fruit's bestowed powers, as used by Bellamy, have been used primarily for combat. Prior to the timeskip, the basic concept of Bellamy's usage of this power is to turn his legs into springs and then launches himself as a projectile, with his fist held in front of him to punch an opponent at heightened velocity, and he heavily relied on this power for his combat style. Outside of combat purposes, the fruit's powers have been seen being used by Bellamy to jump to the top of a tower where Luffy was calling out for him.
Spring Snipe (スプリング狙撃（スナイプ）,Supuringu Sunaipu?): Turning both his forelegs into springs, Bellamy launches himself directly at his opponent with a punch. This was first seen being used on Shoujou when Bellamy and his crew attacked the Saruyama Alliance leaders. While doing this attack, Bellamy inadvertently also broke the Going Merry in half. In the FUNimation dub it is called the Spring Sniper.
Spring Hopper (スプリング跳人（ホッパー）,Supuringu Hoppā?, literally meaning "Spring Recoil Man"): Bellamy's ultimate attack. Using the surrounding geography like the buildings in Jaya's square, he bounces from one spot to the next, increasing in speed with each successive spring, while also disorientating opponents with the continuous sound of springing. He keeps increasing his speed to such a level that he seemingly disappears to spectators. Then he simply has to aim himself fist first at the target and let the accumulated momentum do the rest. This is the technique Bellamy used to kill Roshio and was first properly seen when he battled against Luffy. Unfortunately, this technique is weak against opposing blows, and Bellamy was defeated with one punch.
After the timeskip, Bellamy's style of usage of the power seemingly changed somewhat, such as enforcing his punches by turning his own arm into a spring, as well as evading an enemy by changing one leg for a quick evasive maneuver. He is also able to change both of his legs into one single spring to supplement his acrobatic skills, and utilize his spring-arms as extensions, similar to Luffy's rubbery arms.
Spring Death Knock (スプリング死拳（デスノック）,Supuringu Desunokku?, literally meaning "Spring Death Fist"): An attack similar to Luffy's Gomu Gomu no Pistol, Bellamy turns his arm into a spring and compresses it. He then releases it as a long-ranged and powerful punch. This was first seen used against Tank Lepanto in the Corrida Colosseum.