Disclaimer: Miraculous belongs to Thomas Astruc. Story correct by sdd-writes-things.
Warning: The fanfic is will be mostly canon, but the idea is also to play a little with what-ifs?
Chat Noir never imagined that he would be so relieved with the fact that his lady was wrong. But that was the way he was feeling in the moment. Finally, he could breathe, after so much tension.
When Ladybug accused Gabriel Agreste of being Hawk Moth, a part of him agreed that it could be true. Even though he was his father, Gabriel was never present, always using Nathalie to do personal things for him. Adrien also knew that his dad was ambitious; nobody became the best stylist of Paris without conviction. Gabriel didn't spare any effort to do what he wanted and, since his wife died, he didn't show any kind of sympathy for any other person. Adrien had already questioned himself many times if his dad was a good person.
Still, he didn't believe that Gabriel was Hawk Moth. He was his father. It couldn't be him. Why would his father waste time doing that? He wasn't gaining anything destroying Paris. And even if he got the miraculous, what good would that do? There was nothing for him to gain and Gabriel wasn't a person who wasted his time doing meaningless things. Time is money, he always said. And Adrien also knew that his father wasn't a sadist, he could be indifferent to other people's pain, but, still, he didn't like to hurt others. He just…didn't care. His father wasn't good; however, he wasn't bad either.
Because if Gabriel Agreste was a bad person, what would that say about Adrien? How could be a good person, with such a bad father? Definitely, his father would have already influenced him enough at this point and he wouldn't have a way to escape the web of prejudice created by him. And Adrien didn't want to believe that he was a bad person. Didn't want to believe that he could also hurt others, even though he was doing everything to help.
Besides, if it was the truth that his father was Hawk Moth, Adrien would have to face his own father. He couldn't even question him when he disagreed with an order. Didn't know how he would find courage to physically attack him. Not even when Nino had been akumatized had things been so complicated. It was one thing to stop his friend that been transformed into somebody else and another, totally different, thing to fight against his father, fully conscious of what he was doing. What would hurting his own dad say about him? Adrien never thought that being Chat Noir would demand this of him. He had to choose between his family and doing the right thing.
However, one look at his lady was enough to know that he could really face him if that was the case. He couldn't let her down, running from the fight against their real enemy. He couldn't fail Paris. And, mostly, he couldn't leave her to fight alone. He couldn't let her risk herself without anyone to help her. He couldn't see her hurt, especially if she had gotten hurt as a result of his own weakness. And he suspected that she would need of all the help she could get in that final fight, so he would do everything that he could to do it. They'd been doing this together since the beginning and they would finish it the same way.
He wanted to tell her why he was so sure that Gabriel wasn't Hawk Moth, because he didn't want to accept it. He knew that she would understand, and they wouldn't go after the stylist, at least until they had some real evidence that it was him. He wanted her to understand the reason why he felt so lost with the idea of fighting Gabriel. However, that would mean revealing his own identity, and even though he didn't care about that, Ladybug would never forgive him.
So when he saw his dad akumatized, he was happy. If Gabriel was that way, that meant that Hawk Moth had transformed him, and the villain would never do that to himself, would never risk himself so harshly for nothing, considering that he was always hiding. Gabriel even said how he needed to get the miraculous to Hawkmoth, so it was clear that they were two different people.
Adrien didn't have any problems with fighting him at that time, because he knew his dad wasn't aware of his actions. Chat Noir saw only one more akumatized that he would need to defeat and only got nervous that he would end up revealing his relationship with the man.
And when Gabriel came back to normal, he was so preoccupied with Adrien. He didn't even know that he was so important to his dad. He felt so happy seeing how desperate his dad was looking for him. Adrien honestly thought his absence wouldn't even be noticed, but his father had called him precious. He had felt at that moment that he finally had managed to gain a part of the attention and approval of his father that he always looked for, even knowing that would be a futile attempt. He couldn't even remember the last time that his father had praised him or showed any interest at him without complaining or talking about his obligations as model.
But that day Gabriel had shown how much Adrien mattered to him. Had shown that he would think about his son even after suffering a terrible situation. Adrien was his priority in danger. That meant that he loved him – the mere thought made Adrien smile with happiness. Thus, he could love still. And Hawk Moth couldn't love anybody; for that he would need to have a heart. He was only a monster, empty of basic human abilities. He was crazy. And Adrien's father wasn't crazy.
No, there was no way that Gabriel could be Hawk Moth. Ladybug was mistaken. The heroine was smart, but she couldn't be always right. That had been one of the few times that she had got it wrong. Adrien wouldn't have to defeat his own father. They would find the real villain and they would win.
A/N: This chapter basically didn't have Marinette, I know, sorry. But I wanted to do something about Adrien's feeling of his father being Hawk Moth, because that was what I thought was the most important part of the episode.