Rengoku (煉獄, "Purgatory") is a battle puppet designed by Hiroshi to blend his engineering knowledge with the unique resources and chakra capabilities available in Sunagakure. The puppet is crafted to be both a formidable weapon and a versatile tool for combat, utilizing a variety of fire-based functions and enhanced mobility to ensure it can stand up to intense battles.
The central feature of Rengoku is its flamethrower system, which allows the puppet to emit powerful bursts of flame from its mouth and both hands. To achieve this, Hiroshi uses locally available compressed oils—resin-based or animal fats—stored in pressurized containers made of reinforced ceramic. These containers are designed to withstand the high heat generated by the flames. The oil is ignited through a spring-loaded flint striker activated by chakra threads. This method provides reliable ignition and eliminates the need for advanced chakra transformation techniques. The flamethrowers in the mouth and arms are capable of unleashing short, controlled bursts of flame, which can be used for both offense and crowd control.
Alongside the flamethrowers, Rengoku also features retractable fire-infused blades in both hands. These blades are made from a combination of heat-resistant materials, including reinforced steel or alloy, coated with a fire-resistant layer. Once extended, the blades can emit flames along their sharp edges through small pores. This not only increases the cutting power of the blades but also adds an additional layer of lethality, as the flames make them capable of severing limbs or burning through armor. The flame emission is powered by the same compressed oil system, ensuring the puppet can generate flames quickly and with precision. These fire-infused blades allow Rengoku to fight in close quarters with devastating slashes that burn through obstacles and enemies alike.
For mobility, Rengoku is equipped with spring-enhanced legs that provide the puppet with increased speed and agility. The springs, embedded in the joints of the legs, are controlled through chakra threads, allowing Hiroshi to adjust the amount of force exerted. This feature enables the puppet to perform quick dashes, evasive maneuvers, and high-speed jumps, which would otherwise be difficult for a puppet of its size. The spring system also helps Rengoku maintain stability on uneven terrain, such as the sandy dunes of the desert or rocky landscapes, ensuring that its movements remain fluid and controlled.
The puppet's joints are designed with ball bearings and reinforced with a mixture of sand-infused oil to reduce friction and ensure smooth movement under extreme conditions. These enhancements prevent the joints from locking or freezing up during intense heat or pressure, which is essential for maintaining its flexibility and durability during battle. The entire body of the puppet is coated with a fire-resistant composite material made from a mix of clay, silica, and carbon, making it resistant to high temperatures and allowing it to withstand prolonged exposure to fire. The internal structure is designed to handle the intense heat generated by the flamethrowers and the fire-infused blades without compromising the puppet's integrity.
Hidden within the body of Rengoku are senbon launchers and compartments for explosive tags. The senbon launchers allow Rengoku to fire small needle-like projectiles, which can be soaked in flammable oil to ignite targets from a distance. The explosive tags can be deployed at strategic moments, offering Hiroshi a means of increasing the puppet's offensive capabilities when needed. These weapons give the puppet versatility in both long-range attacks and close-quarters combat.
The puppet's mobility is further enhanced by its lightweight construction. Despite its fire-resistant and durable features, Rengoku remains agile and fast, making it effective in a variety of combat situations. Its spiked feet provide superior traction on difficult surfaces, ensuring the puppet stays grounded even in the most uneven conditions.
Looking to the future, Hiroshi plans to integrate sealing scrolls into Rengoku's design to store extra fuel and components, expanding its range and endurance in prolonged battles. As his skills with chakra manipulation improve, he intends to upgrade the flamethrower system to a chakra-powered combustion system, making the ignition process faster and more efficient. There is also the potential for flight capabilities through the use of chakra-infused heat vents, which could allow the puppet to gain limited aerial mobility, providing more strategic advantages during combat.