"He's actively trying to dismantle his father's legacy and replace it with his own, designed solely to boost his father's enemies."
This part has just resonated with a good idea.
Why would Adrien try to make heroes stronger?
Besides giving Heroes a reason to be relevant and for crime to drop, what if that is his motivation just in the beginning? While he's still fresh out of cocoon as Metamorphosis and has not yet been figured out by Nathalie, THAT is his reason to do it. Paired with his emotional breaking down over being son of Hawkmoth / emotional distress of all the truth, no wonder that the kid is in a very bad mental place where doing bad things and being found out, and then most likely killed of as a freak of nature is a good enough outcome.
His mental state is very "I'm not expecting to reach 18" so he just gives it his anxious all. Using his powers and going out night after night eventually gets to him, he starts running on fumes both as Adrien and Metamorph. That is the time when Nathalie figures it out, because he falls like a sack of potatoes in the attic, she rushes there and finds Adrien unconscious and detransforming before her very eyes as the lift hasn't even reached the top.
She intervenes and takes miraculous away from him for the recovery (worried Nooroo's idea) and there is a lot of talks, mainly her trying to steer him away from the life that led his father to death, but he takes none of it. He saw that with a villain out and heroes active the crime is down, people are safer, politicians actually follow through with what was promised, plus it's not like his life matters, he's not even human.
What they do agree on, or rather what Nathalie managed to push through the thick skull of his, is that this can't go on like this. He needs help, and Nathalie just can't leave him alone, or trust anyone else to be beside him, so she steps up. They go through his fathers notes and plans, first as Gabriel Agreste, and only then as Hawkmoth.
That's when it all clicks, because should they go only through his supervillain documents they would never notice the connections with many powerful people and organisations.
While he was still Hawkmoth Gabriel waged a silent, behind-the-scenes war on Kingdom, a gang of ultra-rich monsters who wanted to reshape the world how they saw fit. That is what pushes Adrien to become a third side in everything. He will fight the heroes to keep them relevant, and he will slowly make them all stronger so that one day they would be powerful enough to take down the Kingdom.
Until that day comes, he as Adrien Agreste will keep them in check and collect as much info as he can. With this he has a thing any good writing, no matter how unhinged, needs, and that is Reason.
That, and I love a good manipulator character. Imagine the internal conflict each hero feels when it comes out that not only Metamorphosis knew all their identities and was toying with them, but this whole time there was a terrible threat and he was training them for it. Their sweet, sweet Adrien who wouldn't hurt a fly turned out to be someone they would've never defeated if it wasn't for the circumstances.
All their war was nothing but a playground, a chess game with known outcome, a tutorial on how to deal with monsters who won't stop at anything to get what they want, monsters who will care not for them being children, care not for lives lost in pursuit of their goals.
And once again, it was Adrien. Fucking Adrien who still can easily defeat any and each of them alone, and even in groups he is not to be underestimated. Alya might drop journalism for good after this, because Paris #1 villain turned out to be her bestie. It takes both Adrien and Nino convincing her not to.
Nino is pissed and tells her to continue just to spite this world, to spite Adrien, to become better. So much better, that one day no secret would fly past her unnoticed. She didn't become great hero in a day, she won't become great reporter in a day too. She made mistakes as both Rena and Alya, but they don't define her, she's just human like any of them. Adrien interrupts to say that not all of them are human and the rest would look as if he started talking in colors instead of words.
Adrien will tell her how much she stressed him out because she was awfully close to figuring him and his plans out. If she should be angry at anyone, then it's her partners because its them who led her to wrong conclusions.
Alix is just doing what she does best, sitting down somewhere behind Adrien, but in a strategic place. Just like she rubbed off on Adrien, so did he rub off on her. Now she's hyper aware of her surroundings, making plans and routes for escapes, looking for attack clues. It's obvious that everyone is tense after the truth dropped on them, and they all are still pissed at Adrien. That's why this time she's near him, ready to snatch and run should the shit hit the fan.
Or, she supposes, she could do something else.
"Took you fuckers long enough. I told you they are much more stupid than you thought."
"And who the hell are you?" Tigress asked, suddenly remembering that Timebreaker exists and getting into the stance.
"ThEy ArE hErOeS, tHeY dEfEaTed HaWkmOth. Too soft of heart and dumb of ass you lot are." With that she took of her helmet and jaws dropped once more.
"Voila! Finally! It took me almost killing each one of you to make you understand I was a threat!"
"Frankly I agree." Adrien, ever observant and ever the self-sacrificial shit, said to turn attention back to himself. "With how much you are swearing in and out of mask I was thinking you'd be the first to be figured out."
"Adrien... And Alix... Are the villains we fought for the last year.... I am fucking done. I'm a disgrace to reporter-kind. Pantheress, please Cataclysm me."
"Wait, you guys still don't know eachother's identities?" Adrien asked as Alix bent over cackling as a maniac.
"HAHAHAHAHAHA! Two-ha-ha, two, long ass years! And you still don't know! Hahahaha!!!"
"Cut them some slack, Alix, not everyone is as unhinged as we are."
"Phoo, joining you was the best decision of my life!"
"And don't you forget it."
"Oh, I won't, handsome! Com'ere." Marinette's jaw fell even lower than low when pinkette kissed him.
"I say we wipe their memories and see how long it would take them figure it out on their own." Her hands were still around his neck, and his glided to her waist as he leaned for another kiss.
"Promise?" She gently pushed their foreheads together.
"Promise." He said closing his eyes and savouring the moment.
"I will hold you to that promise."
"EXCUSE ME?! WHAT THE HELL?!" All eyes turned to Marinette.
"S-since, since when! A-are you two..are, are!"
"Kissing? Dating? Loving?" Alix teasingly provided.
"You. My best friend. Have been dating HER." Nino asked in disbelief at yet another betrayal.
"Mister Agreste, you are fucking dead to me."
"Says the man who still won't admit he's dating Alya."
