(Capcom's primary storyline)
"I am the National Security Advisor. It's my job to prevent terrorist attacks, not cause them..."
The Family and Ada Wong
"How could she leave me? We were the perfect partners! She was beautiful, intelligent, and the only one I would allow at my side. She should have known that!!!"
Carla Radames and Project Ada
With Ada Wong in his life once again, Simmons dedicated himself to "programming" her. He had to make sure that she was like Ada in every regard. That was except for one thing - he had to make sure Ada would never leave him again. Everything went just as Simmons had hoped as the new Ada exhibited the same intelligence and mannerisms as the woman he remembered, though this one loved him implicitly. While Simmons was completely unaware his new Ada was beginning to have internal conflicts with the small bit of Carla Radames that remained in her very being, he showered her with her own responsibility by giving her a submarine base and complete control of The Family's East Asia soldiers. Unknown to Simmons, Carla's true persona resurfaced; angry with what he did to her, she set out to undo everything he believed in.
Agent Sherry Birkin
"Her overly-kind and ultimately naive, charitable nature makes me sick. But, she could still be of some use."
Betrayal in Edonia
"My dearest Ada Wong... Jake Muller has been located in the Republic of Edonia. Your mission is to find out if his body has antibodies to the C-Virus. We cannot allow a vaccine to be produced. Agent Birkin will be sent in to acquire the target. Your job is to ensure they escape the country alive. Good luck."
Assassination of Adam Benford
"Now he has made an enemy of The Family and there is no turning back. It's time I use my position to make sure balance is kept in this world."
The plan could not have gone any better as Helena's attempts at pinning the blame on Simmons were easily scoffed off with his high-ranking position. Furthermore, the involvement of Adam Benford's close, personal friend, DSO agent Leon Kennedy, gave Simmons another scapegoat for the crime of the president's assassination. Now in control, Simmons put the Sterilization Operation into motion again with the intent of destroy Tall Oaks and any evidence against his involvement in the process. Simmons received a call from someone he hadn't heard from in a decade - the real Ada Wong. Ada revealed to him that Carla was hellbent on bringing down the global political order, all for petty revenge for ruining her life. Simmons left for his private jet to head to China to confront Carla, receiving yet another unexpected call; Sherry Birkin and Jake Muller were still alive, having been experimented on by Neo-Umbrella for the last half-year.
Believing the situation to be taken care of in Tall Oaks, Simmons set up a personal rendezvous for Sherry and made way for China to confront this situation. Albeit after his departure he was aware that U.S. agents Leon and Helena were following him - despite F.O.S. coordinator Ingrid Hannigan putting forth a false report of their deaths - he had made sure to provide orders to have them disposed of so they were no longer a concern. Unfortunately, the delight of the situation in America was ruined by something he had never considered - a bio-terror attack had occurred in China utilizing the C-Virus. Simmons could see his world crumbling around him as a terrorist organization calling themselves Neo Umbrella took credit for the attack.
"He had to be stopped! He was leading my country, and this world, into complete chaos!"
He was contacted by Carla shortly after as she relished in what she had done to him and done to the stability he and The Family had fought so hard for so long to maintain. Noticing Leon and Helena still attempting to either capture or kill him, his anger only increased at the thought that they would rather pursue him - someone who, as he felt, was trying to do what was right for his country - as opposed to at true terrorist like "Ada Wong." He then revealed his motivations for killing Benford but Helena retorted that he caused one disaster to avert a possible one at the cost of innocent lives. Succumbing to his infection as the enhanced C-Virus consumed his body, his entire structure began to split and fracture until his body ultimately mutated into a horrific monstrosity resembling a quadruped. Simmons proceeded to battle both agents aboard the speeding train, believing himself to have the upper hand with his new mutation. However, the two managed to eventually wear him down until he reached a point of vulnerability, particularly under the realization that The Family intended to leave him to die and simply replace him. He attacked in a final attempt to kill Leon and Helena, but a single well-placed shot from Agent Harper caused him to lose his balance and fall under the train. The two abandoned the derailed train cars, leaping into the nearby ocean as they believed Simmons to be finished.
However, the severe infection from the potent virus made Simmons incredibly resilient and he survived his injuries. Although his spirit was deeply damaged, Simmons made his way to the Quad Tower where Project Ada had begun so many years ago. It was there that he confronted Leon and Helena, having already killed the BSAA agents guarding the building, and letting the zombies inside to infect the survivors. As an added surprise, the real Ada Wong made her presence known in a helicopter to provide aid for the two agents. Believing her to be Carla, Simmons accused her of taking Jake Muller away. Simmons' mutation overtook his body again, this time mutating him into a massive behemoth resembling a theropod dinosaur. Completely consumed by only the most basic of instincts - to hunt - Simmons attempted to kill the three, even throwing the weight of his body at Ada's helicopter to destroy it, as well as destroying a BSAA truck and killing its driver when he tried to aid them. Derek's body painfully reverted to its human form several times throughout the battle as he sustained more damage until he finally collapsed in his mutated body, succumbing to his wounds once more. Ada made her escape as Leon and Helena followed her up to the roof of the Quad Tower.
The End of Simmons
"Stay away from her, Leon! You're not half the man she needs! Come with me, my love. We'll be together, forever!"
Simmons continued his attempt on Leon's life, surviving Ada's attempts at killing him. He followed Leon and Helena to the roof of the Quad Tower where his new mutation allowed him to absorb the living corpses created by the C-Virus gas to regenerate damage he had sustained. His first attack was short-lived as Leon and Helena managed to weaken him to the point where a small swarm of zombies that had surrounded them began to feast upon his mutated body. Simmons took advantage of this, absorbing the zombies. Newly mutated for the final time, Simmons made another attack in his massive form resembling a strange combination of different insects. He tried to dislodge a tram cart Leon rode, but was unsuccessful until he cornered the two agents just outside of the heliport. Battle ensued and seemed like it would go on until his prey was exhausted as he continued to regenerate any damage sustained by devouring surrounding zombies. However, a lightning rod that had broken loose during Ada's landing scenario came into play and the agents managed to trick Simmons into devouring a zombie with the rod impaled through its body. As Simmons regenerated part of his damaged head, the lightning rod became embedded in it after he had devoured it, drawing in a massive lightning strike from the storm overhead. In the moment of freedom, Leon and Helena reached the helicopter Ada left for them to escape in until Simmons made his final attack attempt. A rocket launcher left as a gift, as well, was fired at Simmons by Leon, dislodging him from the roof of the tower and sending him plummeting below.
Simmons fell against the walkways, breaking apart, and leaving his broken human form clawing in defiance. As the separated flesh combusted, Simmons was impaled upon the obelisk in the courtyard at the center of the tower where he had confronted them earlier. Derek tried futilely to mutate again, but lacked the strength as the wound sustained slowly bled him out until he finally succumbed to death, his blood flooding the courtyard's floor, ironically forming the logo of the Umbrella Corporation, symbolizing that his actions were just as evil as Umbrella's.
Afterwards, Leon and Helena discovered a data chip left behind in the helicopter by Ada that contained the evidence they needed to clear their names and prove Simmons' guilt.
Skills and abilities
Inherently, Simmons had no particular set of skills. He seemed to be extremely intelligent, or at least claimed himself to be, and capable of orchestrating grand plots. The only real semblance of power for Simmons came through in resources. As the head of The Family, he had nigh-limitless resources at his disposal in terms of funding, research materials, scientists, locations, and soldiers. As an official government employee of a high rank, being the National Security Advisor, he also had another source for various resources such as the command over government agents such as Sherry Birkin. Although he ultimately had nothing personally, he was extremely capable at finding ways to manipulate any situation to his advantage.
Upon being infected by Carla, Simmons gained several superhuman powers. He retained at least most of his intelligence to begin with although his declining sanity and mental stability made this questionable. As part of the enhanced C-Virus, he was able to transform into multiple forms with varying powers. His first and primary form was that of a quadruped, often with an extension from the front that made it resemble a centaur as his more human body and face were exposed. In this form, he was able to turn small shards of his bone matter and skeletal structure into razor-sharp projectile weapons, He coud also conjoin and compact said mass into a deadly Spear/Razor blade that could easily rip through steel & flesh. The regenerative capabilities of the virus would allow him to heal the damage sustained to his skeleton from this, giving him nearly limitless ammunition. His second form was more based around its sheer size and incredible strength. His final form - that of a colossal amalgamation of insect species  - was also capable of feeding on infected biomatter such as zombies which enabled him to regenerate damage his body had sustained.
Personality and relationships
Prior to his meeting with Ada, Derek was described as someone who was clear-thinking and extremely capable. However, ever since losing Ada Wong he had declined in mental stability, growing more maniacal and unstable. He was ruthless and uncaring of most people. He found Sherry's charitable nature sickening and disgusting and showed no reservations about killing tens of thousands of innocent people, including the president, just to maintain stability. This did, however, show one particular fondness of Simmons and that was to his country. He seemed to honestly believe that everything he did, no matter how evil or uncouth it was, was for the sake of preserving the country in its entirety. Simmons believed his existence is important to the world, having told Leon and Helena they have no idea what would happen if he dies.
His closest relationship was to that of Ada Wong, although it was a one-sided and unrequited one. He became obsessed with the woman who could, under his claims, match his own intelligence. This resulted in him attempting to replicate the woman after she had exited his life, ultimately taking advantage of the young Carla Radames to gain what he wanted. As Carla had become a newly formed Ada, it also provided more insight to how far gone Simmons' sanity had gone, honestly believing this new creation to be Ada Wong all the way up until his death. Prior to her transformation, Simmons saw great promise in Carla's abilities and had employed her for the purpose of developing bioweapons. Although she was emotionally attached to him, he did not reciprocate her feelings (at least not until she had become "Ada Wong"), though was not hesitant to use these feelings against her for his own personal gain.
- ↑ 1.0 1.1 Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Derek C. Simmons.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). Scene: To China. Level/area: Leon Chapter 3.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Ada and Derek.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: The Family.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Tall Oaks Cathedral and the Underground Lab.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Two Ada Wongs.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Submarine.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Life without Freedom.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Carla Radames (file).
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: A Deal with the United States.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Report on Jake Muller.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Ada Wong.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Helena's Crime.
- ↑ Capcom. Resident Evil 6. (Capcom Co., Ltd.). File: Derek's 3rd Transformation.