Devouring Flames
It was scientifically theorized that consuming another ghoul would allow the consumer to absorb the RC cells of the one being eaten and with a high enough concentration of RC cells, a ghoul would be able reach a form very few of their kind ever reached: Kakuja.
However, the scientists that studied the ghouls were wrong.
They couldn't be faulted. They simply lacked the knowledge of the Deathperation Flames' existence. The knowledge of the Dying Will Flames, had it been known, would have changed everything.
There is one question that has been asked over and over: Why can ghouls eat only human flesh? What is so unique about human flesh that it does not cause harm to the ghouls who devour it?
It is because everything unique about ghouls is made to consume and utilize Deathperation Flames. Everything. From their stylized tastebuds and unique enzymes to the high concentration of RC cells present within their bodies.
Humans are the only creatures that are naturally able to produce Dying Will Flames.
When ghouls devour their meals, what they taste mainly is not the various chemicals that make up a human's palette, but the Flame type, mix, density, and purity present within the flesh. Although the Flames' presence allow ghouls to process the flavor as humans can, because raw meat all taste mostly the same, many do not realize this. Their main difference in taste stems from the difference in Flames. This is why Ghoul Restaurants operate as they do. When hunted, the Will to survive stokes the victim's Flames, causing a more intense and flavorful meal.
The process does not stop there. Ghouls possess unique enzymes which draws out the Flames to store them into RC cells. It does not matter what state the meal is in. The flesh can be soft from still alive prey to stiff from rigor mortis. As long as Flames are still laced in the meal, anything can be digested.
The RC cells store the Flames to power the ghouls' bodies and kagune. It is not any unique physical material in the kagune that is able to damage the skin that is known to be able to break steel. The cells can be grown in a lab, after all. It is the Deathperation Flames running through the kagune that causes harm to ghouls. Quinques can only be made from kagune because of the Flames running through it.
Ghouls who consume enough Flames to have an extreme excess causes their RC cells to mutate and their kagune to change into something akin to armor. This new kagune gives its wielder immense strength, but while it benefited its user on a physical level, its most notable aspect was the toll it took on the wielder mentally.
As Deathperation Flames are produced in times of heightened Will and near-death, they capture and contain traces of the thoughts and emotions and Will that birthed them.
Run.
Run.
Fear.
Fear.
Desperation.
RuN!
Why is this happening to me?
Demon!
Monster!
FeAr.
Anger.
Anger.
Hate.
Hate.
HaTe!
MaY yOu RoT iN HELL!
The kakuja often times made the wielder lose absolute control of themselves when they used it and, more often than not, made the ghoul certifiably insane.
Though there are some cases where ghouls have been able to maintain control of their kakuja during its use, those cases are usually uncommon. Those ghouls who do not lose themselves to the remnant Wills inside the Flames, however, are to be feared.
After all, their drive and determination are the likes that are able to subjugate the Wills of hundreds and thousands.
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AN: I need more KHR/TG xovers! Very grateful if someone decides to take this up and write it.
Seriously, feel welcome to play around in this universe. I wanted to write a fic in it, but all I managed were fragments and dialogue that I couldn't connect.
My thoughts were somewhere along the lines of humor with Chef Tsuna (under Reborn's direction) realizing that Flame induced food tastes better, eventually giving some to thank Aneiku for helping him with something. At his insistence and being polite, they ate some and realized it actually tasted good and boosted their powers. Cue spread of information, ghouls competing for favor, kidnappings, realization that oversea ghouls are thought of as diseased humans who are Flame deficient (aka they all work for Mafia). Vongola claimed Japan as theirs, causing a lack of Flame active individuals, thus, no one connected "cannibals" with the "Flame deficient." Cue artificial kagune, mass smuggling of ghouls, and Dove confusion. Somehow, besides the humor fragments, the story became so dark.
The storyline doesn't have to be as above. I'll be happy if there is just more stories.
Inspired by 2 things: me thinking that Byakuran's "wings" and Touka's kagune look very much alike (Byakuran must have learned how to make artificial kagune) and Dandelion-san's "The Epic Rivalry Between Sasagawa Kyoko and Sawada Tsunayoshi"