A/N: This is what happens when you can't sleep at 4 am, and you have a recurring plot bunny that won't leave you alone. WARNING - major plot spoilers for Season 4, up through Ephemeral.
Stop making decisions out of fear
Su-Han, the Celestial Guardian of the Miraculous, wanted - no, demanded to know Chat Noir's secret identity after he wasn't able to show up to an Akuma attack, and wasn't pleased that Ladybug didn't know it. She didn't really know what had happened to her plan to use Viperion's "Second Chance" ability to learn Chat's identity, then erase it from her memory, but something major must have gone wrong because time was all messed up and it meant that she and Chat had to fix a GPS satellite. In no uncertain terms, Ladybug told the ancient Guardian that he was letting his fear control his actions. Now Ladybug and Viperion were in the sewer tunnels so he could turn the snake Miraculous back to her care.
Luka was just about to detransform, when a thought occurred to him. Ladybug didn't know it, but he already knew both Chat's identity and hers, and he also knew how much the two superheroes were pining for each other without knowing it. So he took a chance.
"Ladybug, something you said to Su-Han got me thinking."
"Oh, really? What is it?"
"You said that the reason he was demanding Chat Noir's identity was because of his fears."
"And he is."
"Well, I think you should take your own advice."
Ladybug huffed a little. "What do you mean?"
"I mean your plan to discover Chat Noir's identity," Luka said as he de-transformed. "Instead of just letting Chat know what was going on and letting him help you, you planned to use Second Chance to learn his identity, then forget it. And the consequences were dire, Ladybug. Just look at how exhausted Sass is."
Ladybug crossed her arms and stared at her former boyfriend, even as she studied the little snake Kwami. "Your point?" she asked as she held her hand out for the miraculous.
"The point, Ladybug, is that you are afraid."
"Of what?"
"I don't know exactly, but I have a few guesses based on your inner melody. You are afraid of being the Guardian."
"I was given guardianship in the heat of battle. I didn't have much choice."
"Ah, but you are afraid to share that responsibility. Why not share it with Chat Noir?"
"I can't."
"You can, but you won't. Anyone who knows you knows that you have feelings for Chat Noir that you are afraid to face."
"Why does everyone think I'm in love with Chat Noir? I'm not!" she denied. "He's my best friend and my partner, and I couldn't be Ladybug without him. But that's all."
"I never said anything about love," Luka gently reminded her as he touched her shoulder. "But there is obviously something in your relationship with Chat that you are afraid of. And it's hurting your relationship with him."
Ladybug gasped. She hadn't told anyone about Chat Blanc, but it was true that he still haunted her nightmares.
"From your reaction, I'll guess that I was right. Something about Chat Noir is troubling you, and you are afraid to talk to him about it. So take your own advice, Ladybug, and stop acting out of fear." He smiled as he handed the snake bracelet back to Ladybug. "I bet you are letting fear prevent you from doing at least one thing in your personal life as well."
Shock on her face and tears forming in her eyes, Ladybug looked at the departing teen. "Thank you, Luka," she whispered. "I'll think about it."
A/N: In my head, I see Marinette going home and thinking about all the decisions she's made since becoming Guardian, and realizing how many of those were made because she was afraid.
I also see her talking to Sass, who agrees with Luka that she should have simply told Chat Noir that Su-Han wanted to know his identity.