RB-Formula

RB-Formula aka Red Beast Formula is a drug that was originally developed as part of a super soldier program by Marcus Carlson in 1932 during the second World War, the drug was eventually perfected in 1938 and caused Marcus to become insane after taking a dose.

Many years later, the same serum was further modified by crazed scientist Dr. Kobayashi Idagawa who ultimately used it on Akane Hitarashi to transform her into the monstrous Yajukon.

History
Wanting to turn the tide of the war in 1932, Captain Marcus Carlson enlisted the top scientists to band together in order to create a serum that could produce a super soldier that could assist on the battlefield. By 1934, numerous test subjects of the formula go insane and are exterminated as a result which only angers Marcus.

The serum is perfected in 1938 and Marcus impatiently takes a dose, causing him to become insane and turn on his own soldiers in order to form his own organization known as Corvus.

Many years later, shunned scientist Dr. Kobayashi Idagawa used the serum and modified it by adding various types of animal DNA in order to make it stronger. He used this particular variation on an innocent schoolgirl named Akane Hitarashi which transformed her into the monstrous Yajukon.

Blood containing the RB-Formula was extracted from the Yajukon during containment within the Corvus HQ, it was then exposed to the energy of the Sikring of Control before being used to mutate Mary Craige into a super weapon dubbed the Brawler.

Characteristics
When the serum was first concocted in 1932, it proved to be too dangerous on humans due to causing them to become animalistic and lose their humanity while gaining in strength. The RB-Formula gave the specimen red accents in their hair, and made their eyes become bloodshot red which earned it its name.

The "perfected" variant had toned down side effects, as it only caused Marcus Carlson to go mentally insane and turn on his own soldiers while also giving him yellow, slit-pupil eyes and increasing his lifespan.

Kobayashi Idagawa's rendition of the serum was heavily modified, and contained various animal DNA which resulted in Akane Hitarashi's transformation into the uncontrollable Yajukon, giving her enhanced abilities, sharp teeth, yellow slit-pupil eyes and blood-red hair.

When Corvus used their rendition of the serum on Mary Craige, she went through a similar transformation into the Brawler but instead gave her glowing purple eyes and black hair with grey streaks.

After the Brawler had extracted some of the Yajukon's blood, it caused the Yajukon's eyes to turn more human-like and red, while also decreasing her animalistic behaviour.