Engine

Engine (エンジン) is the Quirk used by Tenya Iida and Tensei Iida.

Description
Engine grants both Tenya and Tensei engine-like protrusions somewhere on their bodies that allow them to move at extraordinary speeds.

Thanks to Engine, Tenya and Tensei can both dash through long distances in a short amount of time. This makes them suited for missions that involve reaching a faraway place as fast as possible, chasing after an object moving at high speeds or even escaping from an overwhelming threat.

The mufflers found on Engine can be removed, with new ones regenerating in their place over time. These new mufflers may increase in power and efficiency, assuming the user puts themselves through massive strain due to Quirk usage, as Engine will naturally adapt to the newfound intensity.

The two Iida brothers have access to Recipro Burst, a Super Move that grants them a short-timed, yet immense burst of speed. This move overheats their engines, forcing them to undergo a cool down period right after performing it.

Weaknesses
Engine appears to require fuel in order to work properly, similar to an actual vehicle. In Tenya's case, he drinks orange juice as a source of fuel for his Quirk, while carbonated drinks make him stall. Tensei appears to favor grape juice instead. If they don't refuel themselves, their Quirks will gradually lose potency until it stops functioning altogether.

Tenya Iida
Tenya's Quirk manifests on his calves, largely increasing the muscle mass of his lower legs and requiring exposure to not clog. Also, the exhaust ports appear able to extend from his calves before and while in use and retract back afterwards.

Those engines give Tenya massive leg strength when activated, resulting in increased kicking power. Consequently, Tenya's fighting style ends up revolving around fast and powerful kicks, which are strong enough to crush even metal.

Furthermore, he can adapt to the situation at hand by switching between gears. There are at least three confirmed gear settings, but he needs to go through each one in proper order as he accelerates further. Tenya once observed that he could only switch up to third gear for a 50-meter dash, implying that he needs more distance to achieve his maximum speed.

As part of his training, Tenya engaged in hardcore, long distance running to increase his leg strength and stamina, so that he can run faster for longer periods of time.

Sometime after the Provisional Hero License Exam Arc, Tenya was told by his brother Tensei that there was a method to improve his Quirk, which the Iida Family has been using for at least three generations. By removing his mufflers and then going through intense training, Tenya was able to grow new mufflers that could allow him to reach even higher speeds while consuming less fuel.

Jamming the mufflers of his leg engines will cause them to stall and is left unable to be used.

Named Super Moves

 * Recipro Burst (レシプロバースト): This move allows Tenya to forcibly accelerate his Quirk, greatly enhancing his speed for 10 seconds, but at the cost of disabling his engines for a short period of time. Even Shoto Todoroki could not fully evade Recipro Burst and admits that he expected no less of its incredible speed.
 * Recipro Extend (レシプロエクステンド): After Tenya manages to cool down the negative effects of Recipro Burst, he gains even more acceleration than before.
 * Recipro Turbo (レシプロターボ): After removing his mufflers and allowing new ones to grow in their place, Tenya became able to accelerate his Quirk and greatly enhance his speed for 10 minutes. The speed this Super Move grants is faster than Recipro Burst and Recipro Extend, rivaling even Jet.

Tensei Iida
Tensei's Quirk gives him two exhaust-like engines at the end of his elbows.

Because his engines are located in his upper body, Tensei is capable of boosting himself vertically, allowing him to acrobatically climb up walls as well as hover slightly. Despite this, Tensei is perfectly capable of propelling himself forward, letting him cover long horizontal distances just like his younger brother. It's unknown if he has to change between gears like Tenya.

However, Tensei has noted that he can't make tight turns properly when at high speeds, meaning that he has to slow down in order to do so. Also, if he crashes into walls while at top speed, it may result in him seriously injuring himself. As such, he has an airbag system installed into his costume for safety.

Because Tensei knows about the Iida Family's secret method of Quirk improvement and told his younger brother about how to do it, it's implied that he went through the same process of improving his mufflers.

Named Super Moves

 * Recipro Burst (レシプロバースト): By over torquing his engines, Tensei is able to produce an explosive burst of speed. This also causes his engines to overheat.
 * Rocket Charge (ロケットチャージ): Tensei's hero costume increases and focuses his engines' output, affording him greater acceleration and launching him into the air, like a rocket. This causes his engines to stall.

Trivia

 * Tenya's manifestation of this Quirk is similar to Jet, as both grant the user propulsion devices in their lower bodies that provide enhanced speed. The main difference is that in Jet they are located at the bottoms of feet and provide enhanced jumping, while Engine has them located in the calves and provide enhanced running.
 * Like several other Quirks, Engine has its own signature sound effect: "DRRN".

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