(Will not add more, this is enough, Deku can out think almost all of these)
Weaknesses:
Speedster weaknesses:
The only weaknesses listed below are the ones that differ between the Negative Speed Force and the Speed Force. For all of the weaknesses that a speedster can have, see Speedster weaknesses.
Like with the Speed Force, speedsters may show one or more weaknesses despite their connection to the Negative Speed Force.
Gravity: While deprived of gravity, a speedster's lack of weight prevents them from accessing their speed.
Tachyon production: Users of the Negative Speed Force produce huge traces of negative tachyons while running, which can easily be tracked.
Negative Speed Force weaknesses
The only weaknesses listed below are the ones that differ between the Negative Speed Force and the Speed Force. For all of the weaknesses that a speed force can have, see Speed Force weaknesses.
Like the Speed Force, even though the Negative Speed Force is a powerful, interdimensional force, it still has some weaknesses.
Inability to reform matter: The Negative Speed Force is unable to reform matter. Until the Speed Force reconstituted Eobard Thawne's physical form, he existed within the Negative Speed Force as negative tachyons following the Anti-Monitor Crisis.
Positive/Most Speedster Weaknesses:
Speedsters may show one or more weaknesses despite their connection to the Speed Force. Whether this hints towards inherent limitations of the Speed Force itself or just to limitations of its users' control over their connection to it, is not known for certain, but the latter seems more likely.
Antimatter: The formation of an antimatter wall can prevent the Speed Force from extending beyond a specific point in time, or allowing speedsters to physically travel beyond that point, as seen when Barry Allen, in his attempt to travel to the future and witness the Anti-Monitor Crisis, collided with such a wall and was immediately ejected to his native time. This likely occurred since an antimatter wave was set to hit Earth-1 on that future date, destroying its entire universe and rendering all future dates beyond that point nonexistent and inaccessible.
Cold temperatures: Because speed is produced by a build-up of heat in the target's atoms, speedsters are vulnerable to extremely cold temperatures. It will also temporarily stunt their healing capacities.
Connection severance: The essence of a speedster's powers is their connection to the Speed Force. Regardless of how strong that connection is and how much power they can draw, so long as they are connected to the Speed Force, they can utilize their speedster abilities. If that connection is somehow cut off or severed, either temporarily by the speedster being in a place that dampens the connection to almost nothing, or permanently by some external force (such as operating in "Flashtime" for too long), they will cease to be speedsters and lose their powers.
Electricity absorption: Speedsters' unique biology causes their bodies to produce massive amounts of electricity, which charges their molecular structure and allows them to accelerate their movement. Should a speedster be drained of this electrical energy, they will lose their power. However, the Speed Force is genetically coded to their DNA, meaning they are incapable of losing their potential for enhanced speed. If this electricity is absorbed by another source, all of their powers will be suppressed, including their superhuman healing and accelerated perception. Much like an electrical device, which needs to recharge, speedsters must electrify themselves to a great extent in order to jump-start their powers once more.
Gravity: While deprived of gravity, a speedster's lack of weight prevents them from accessing their speed.
Hyper-metabolism: While moving at accelerated speeds, speedsters burn calories much faster than normal people. This requires them to consume large amounts of nutrients (about 10,000 calories from a single day of exertion) to maintain peak physical performance. Continued usage of their speed while deprived of a sufficient quantity of nutrience will render them disoriented and weak before ultimately passing out as a result of low blood glucose. Also, because of their accelerated healing, they are unable to be given painkillers, sedatives, or anesthetics, as their body's metabolism burns through them too quickly for them to have any effect. Likewise, even a highly concentrated drug or toxin will only affect them for a few seconds before completely wearing off.
Kinetic energy absorption: Because their abilities are derived from movement, the removal of the kinetic energy built up by speedsters will leave them in a state of temporary paralysis. However, if they can build back up enough kinetic energy within themselves, the effect can be instantly negated.
Negative tachyons: If a speedster has negative tachyons in their system, it slows them down and they are unable to access the Speed Force. Nora used a device pumping negative tachyons into her system, which slowed her down and allowed her to pretend like she is unable to travel back to her proper point in the timeline. However, Team Flash later learned that negative tachyons don't just offset positive ones; they actually siphon positive tachyons, allowing their user to parasitically steal speed from the Speed Force, thereby allowing an individual to access the Negative Speed Force.
Resonance field disruption: Speedsters create a resonance field when moving at super-speed, which the Cisco Ramon of 2024 made a device capable of disrupting. The result of this device made a speedster unable to move through time despite moving fast enough to do so, though it is unknown if it is capable of otherwise dampening their powers. Harry Wells designed similar technology capable of causing a decrease or even drainage of a speedster's powers.
Speedster weapon: A special kind of rifle can fire an energy pulse that could render a speedster stunned and cut off from the Speed Force. However, the effects are only temporary.
Temporal alterations: While a speedster's speed allows him or her to break through the temporal barrier, it is not without drawbacks. In addition to potentially causing unforeseeable, damaging changes to the timeline, reckless travels through time can alert the Time Wraiths. These temporal guardians become instinctively drawn to the careless speedster, driven to capture the person who disturbed the timestream and draw the person into the Speed Force with it, although they often prioritize repeat offenders, as seen when the Time Wraiths captured Zoom for his violations of the Speed Force despite intending to punish Barry for creating a time remnant. Also, as seen when Barry created "Flashpoint", reckless alterations any speedster makes to the timeline can also affect the user's memory, gradually making even them forget how events originally were before they'd altered the timeline.
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The Neutral Speed Force Hero
FanfictionDeku is betrayed and meets both Barry Allen (The Flash TV series) and the Reverse Flash who grant him their Speed Force powers, allowing him to generate both Speed Forces for his reality.
