The Gutsu Gutsu no Mi is a non-canon Paramecia-type Devil Fruit that allows the user to turn their body into a blast furnace and melt metals inside it, making them a Blast Furnace Human (溶鉱炉人間 Yōkōro Ningen?). It was eaten by Bill, but with his death the fruit has returned into circulation.
- "Gutsu Gutsu" is the Japanese onomatopoeia for something boiling.
- In the FUNimation Entertainment subs, it is called the Smelt-Smelt Fruit.
Strengths and Weaknesses
The main strength of this fruit is the ability to consume ore, melt it down in their bodies, and then solidify the molten ore in the user's body and shape it into anything the user desires, including metal weapons, which he can pull out from his abdomen. The user can even launch the ore in its molten state to attack others. They can encase people in solid silver by pouring the molten ore on them; the user will also become encased in silver if covered in ore, but they will still have freedom of movement. They are also granted immunity from being burned by the molten ore and the initially hot metal it is formed into. The more ore the user consumes, the larger and more powerful they become, as Bartolomeo pointed out that the resultant effect appears similar to Logia.
It seems that the user requires a supply of ore inside them in order to be able to form weapons, forcing them to constantly consume ore in order to use the fruit. The weapons created from the fruit will also quickly become molten again when it is destroyed. Also, overeating ore would cause the user to exude a tremendous amounts of heat, capable of melting everything around inadvertently. Other than that, the user is also affected by the standard Devil Fruit weaknesses.
By eating ore, Bill can send it into a blast furnace inside his body, which will make his body glow orange and exude steam. He brings out the ore to use for whatever fits the situation, such as weapons for when he is attacking. He also sometimes attacks with molten ore. Additionally, he uses his fruit to also increase the military strength of his entire crew, giving all of them weapons, ranging from blades to functioning firearms.
In more desperate situations, he ate a large quantity of ore, increasing his muscles and to create torrents of molten ore, capable of melting an island. As a last resort, Bill has also been shown to coat his entire body in silver armor. While in this form, he can attack by forming a sphere made of molten ore. 
- The basis of his power has many similarities to Enel's Gloam Paddling, as both use heat to melt metals freely into new shapes.
- This is the third filler Devil Fruit that grants the user control over heat coming from their body.
- Many of his abilities mimic Gild Tesoro's Goru Goru no Mi ability:
- Coating his opponent in metal to make them living statues;
- Turning into a giant metal man.
- Ability to coat oneself in a metal armor, in order to enhance defense and offense.
- Able to make weapons and armor for allies to use.
- Incidentally, many of these abilities are also things that Galdino can use with his Doru Doru no Mi ability, but with wax instead of metal.
- This power is also similar to the Ami Ami no Mi and the Baku Baku no Mi as both also requires the consumption of inedible things to fully use their capabilities, although this one only works with metallic ores.