Genji headcanon with doodle and a makeshift au concept!
(CW: unknown glowing green fluid coming out of mouth ,nose and eyes, death, near death, brief mention of childbirth)
Starting out this before I get into the story of it, out of the three characters you can summon the spirits in OverWatch Genji's is very different from the other two, while Hanzo and kiriko expel the spirits from their bodies Genji almost absorbs his or let it take over his body.
So now headcannon time!
Wild dune hanzo's mother was pregnant with Genji there is unforeseen complications which led to Genji being born very prematurely and to the unfortunate death of their mother. Genji should have died from this but his dragon physically didn't let him, his dragon used whatever power it could to keep him alive and help him survive. And from power used to keep Benji alive from such a young age him and his dragon have a much more intertwined connection and a much stronger connection than any other shimada before him. This at the same time however made his dragon appear smaller when summoned leading people to believe he wasn't as powerful as his older brother or his father. Little did anyone else know the reason his dragon was smaller was because more of the dragon's power was being used to physically make him stronger rather than to keep a larger form for the dragon.
Once again Genji's dragon would help save his life when after being almost killed by Hanzo he should have died before OverWatch got to him, but once again Genji's dragon used whatever power it could to make sure he didn't die, his dragon kept him alive and had been keeping him alive trying to help him survive through his entire time in blackwatch. And due to ever building anger for what happened his eyes were glowing red due to the power from his dragon ( Im pretty sure I had mentioned that before in a different head cannon post)
Eventually wants his body had fully gotten used to the cybernetics and had healed physically his eyes stopped glowing as much, this is because his dragon was now able to focus its magic or whatever elsewhere more attack focused rather than purely trying to keep him alive. And after his training with zenyatta he was able to much better control and work with his dragon and start to unlock his true capabilities.
Back to pulling from in-game stuff, Genji during his ultimate glows the entire time. Primarily with glowing mist or smoke emitting from his eyes along with lightning emitting from his skin. He is able to go faster and hit harder than he would normally. Additionally whenever he Ults Genji's expression in mood is furious and raging the entire time, he has a full blown snarl on his face.
LOOK AT HIM HES SO ANGY
Even more so when actually attacking! (Also don't mind him being massive and tiny in some pictures, i was in a custom game with a friend)
So I imagine whenever he fully summons his dragon for an attack unless he's summoning it like he does in the dragon cinematic where it's out and about doing its own thing, it physically possesses him partially! You still have most of his mental control but it's more fuzzy he's pretty much backseat driving in his own body, as the dragon has taken over complete control has essentially gone "you take a break buddy I'll take it from here" which means he ends up being a lot more powerful during attacks like this, but at a cost afterwards.
Doing this is very draining because the dragons were not meant to take control of the human bodies of their hosts, they can live with in them and be a part of them but whenever they are summoned and are going to use their powers they are outside of the human body in the physical world after being expelled from the human body. But not in this case, in this case it puts such a physical strain on Genji's body that whenever he fully does this it results in something like this after he gains control back.
(here is the trigger warning for the gore part)
He still has no idea what this green stuff is and no one from the clan was able to figure it out. And he hasn't fully summoned his dragon and gone into this form during his time in OverWatch so none of them have seen this side yet, but once they do not only are they freaked out by the fact that you just summoned a dragon and then started glowing and looked possessed but then afterwards started puking up this green stuff that they have no idea what it is.
And after they ask if he's okay once he stops spitting this stuff up, he says he's fine and he has no idea what it is. It could be anything from puke ,some sort of random goo that appears, he hopes it isn't blood. Either way Angela ends up taking a sample and does an extensive medical check up on Genji because she is very concerned about what she just witnessed happen. Even more so when she finds out that's the first time he's done that since his cybernetics, which is why it took so much more of a toll on his body than it used to, before he used to just spit up a tiny bit and maybe a bit would run from his nose but that was about it nothing ever this extreme has happened before.
And this is where it starts tiptoeing more into au territory.
One upside though is even after all this damage has been done to Genji's body, whatever injuries he would stains during this period of time that he's possessed and even injuries from before that are healed and fixed. If he got stabbed while possessed guess he's no longer stabbed because there's no trace of the wound ever being there.
And after testing they believe this green stuff he's throwing up is almost like an excess or the remains or remnant of whatever his dragon creates in order to heal his injuries. And since he has less body to heal it's got to go somewhere.
That's all I've got so far! Still working on the au part of this where it pushes the dragon healing his injuries even further, like maybe after a really bad fight where did you gets injured really badly and probably should have died again from his injuries but he was staying the injuries during the period he summoned his dragon his dragon set out to fix those wounds and somehow ended up doing more than he thought was possible. Resulting in him waking up and no longer having any cybernetics with his body being entirely regenerated to how it once was except for the fact he's obviously older than he was. So his body was like if he had never almost died to Hanzo and is if he kept living after that point. Obviously he freaks out quite a lot, leading to him involuntarily screaming when he looks in the mirror, hearing his cries some of the others including Cassidy run up outside the bathroom door asking if he's okay and what's wrong. He says everything's fine because he's still very much in shock and lies that there was something that fell and it spooked him and he would just be out in a minute and would be fine, cut to him coming out the bathroom now wearing his helmet along with all his normal clothes but with the addition of gloves, scarf, and a jacket on top of his hoodie basically covering anywhere is cybernetics would normally be showing.
He tries to be inconspicuous about it but that goes immediately out the window considering the fact he looks like he's dressed to be going out in a blizzard in the middle of summer in Gibraltar. And after much questioning he eventually admits that something is wrong and he doesn't know what happened, and then takes off his mask along with all the additional clothes leaving his hoodie and joggers and stuff. Which everyone else then joins him in the freaking out over the fact that not only are his scars gone that used to cover his face back and remaining fleshy parts but now his limbs are back?!
That's all I have I just thought it would be funny to imagine him freaking out over this, especially at one point where he's just like "god dammit I spent so long accepting who I was and coming to terms with my cybernetic body that this doesn't feel like me anymore I feel like I've been putting someone else's body again!!!"