Basically my theory on what happened to Adrien's mother. Hope you enjoy!
For the purposes of this fanfic, I've named Adrien's mother Lorraine.
Disclaimer: I don't own Miraculous Ladybug.
Cat Noire
...20 years ago...
It was a long and dangerous battle but finally, Ladybug and Cat Noire had done it. They'd trapped Hawk Moth in a sealed room within Notre Dame where no one could find him. Now, the two young woman sat high up on the Eiffel Tower while looking over the Seine together.
"It's really over? We'll never have to be Ladybug and Cat Noire again?" the current Ladybug asked.
"I'm not so sure about that, L.B., Paris may need us again some day," Cat Noire said as she got to her feet "But for now, we can focus on our real lives,"
Ladybug brushed her red streak of hair behind her ear as she and her friend looked out over Paris for the last time as Ladybug and Cat Noire.
...15 years ago...
After waiting 9 months, Lorraine Agreste could finally hold her baby boy in her arms. He was a few days late but now she could look at his chubby little face. Gabriel sat on the side of the hospital bed, looking down at his wife and new son.
"Welcome to the world, Adrien, we've been waiting to meet you," Lorraine said as her son looked up at her.
He grumbled and squirmed before letting out cries of discomfort. His mother held him close to her heart and gently rocked him back and forth. The ring she wore on a chain around her neck fell onto Adrien as Lorraine comforted him.
"Look at him... He looks so much like you," Gabriel pointed out "Same golden locks, same bright green eyes,"
Lorraine smiled at him as she gently lay Adrien over her shoulder and lay back on the bed to rest. Childbirth was stressful but now she could enjoy the reward and be the best mother she could be to dear sweet Adrien Agreste.
...10 years ago...
Lorraine had put Adrien to bed when she looked at the news. A person by the name of Space-Warper was attacking Paris and teleporting things away. She looked down at the Miraculous hung around her neck before looking back towards the stairs that led to her son's room. Gabriel was out of town for business but would be back by the morning. She couldn't let a new villain terrorize the city her son was growing up in.
"Plagg... Claws out!" Lorraine declared.
Being Cat Noire for the first time in 10 years felt amazing. She dashed over the rooftops of Paris towards the carnage Space-Warper was causing. From the corner of her eye, she saw the familiar polka-dots of her old crime-fighting partner. The two superheroes looked at each other from their respective rooftops and took out their communicators.
"Long time no see, Cat Noire. How's the past decade treated ya?" Ladybug asked.
"We'll have to play catchup later, L.B., Space-Warper's getting worryingly close to where my son is fast asleep. I'm not gonna let this thing interrupt my baby's sweet dreams," Cat Noire said, glaring down at the villain.
"Wow, you really do sound like a mother. Okay, let's take this guy down!" Ladybug exclaimed.
Ladybug and Cat Noire jumped down from the rooftops with their weapons ready and slipped into their old crime-fighting routines once again. They narrowly evaded Space-Warper's teleportation bubbles and drew the villain away from the Agreste estate. As the battle turned in their favour, a familiar butterfly shape appeared around Space-Warper's eyes.
"Hawk Moth? That's not possible!" Ladybug said.
"He must have used his akuma to possess Space-Warper! This guy's innocent," Cat Noire realized.
"Space-Warper! Get me their Miraculouses! Ladybug's earrings and Cat Noire's ring!"
Cat Noire looked down at her ring as her time began to go down. She had to finish this quick and get home to Adrien before he woke up. Activating Cataclysm, she ran forward and hit the ground beneath Space-Warper. It cracked and broke away beneath them and the supervillain fell into the sewage system below. Cat Noire held onto the edge and attempted to pull herself up.
"Space-Warper, if you fail to get me Cat Noire's Miraculous then I'll remove your power!"
Desperate and frustrated, Space-Warper created a teleportation bubble with so much gravitational pull that everything around him was sucked in... including himself! Cat Noire stuck her staff into the ground and held on but her ring flashed yet again.
"Not great timing, Plagg," she muttered.
"Cat Noire!" Ladybug exclaimed "Lucky Charm!"
Her yoyo spun but what she got was a breathing mask and oxygen tank. Unable to figure out what to do, Ladybug held onto Cat Noire's hands as her ring completely ran out of power. The staff disappeared and Ladybug found herself holding onto Lorraine Agreste, the model wife of Gabriel Agreste and mother of 5-year-old Adrien Agreste. The pull of Space-Warper's final teleportation grew stronger and stronger and Ladybug found her hands slipping.
"Ladybug!" Lorraine yelled to her but when Ladybug looked down at her, she saw the tears and sad smile "Look after Gabriel and Adrien for me!"
With that, Lorraine grabbed the polka-dotted oxygen tank and breathing mask and her hand slipped from Ladybug's. The point of the teleportation event was to get rid of Cat Noire so as soon as it got her, it's purpose was fulfilled. Lorraine put the breathing mask over her face and hugged the oxygen tank to her body as she was pulled towards it. The moment it had her, it closed and debris fell to the ground all round them.
Ladybug got to her feet and stared down at the ground, gasping in air as she failed to comprehend what had just occurred. She looked down at her clenched fist and opened it to reveal the Cat Miraculous sitting in her palm.
...1 year ago...
Adrien sat at his desk, clicking through computer files containing photos of his long-missing mother. As far as he knew, he had just woken up one morning after his father had returned home and found that his mother was gone. No Dear John letter, no note, not even a message on the answering machine. And today was the day she had disappeared; 9 years ago. There was a knock on the door and Nathalie entered, brushing the red streak in her otherwise black hair behind her ear.
"What is it, Nathalie?" Adrien asked as he clicked off the photo file.
"I've got... something for you, Adrien," Nathalie said.
"Uh, huh... like what?" Adrien asked, paying no attention to the hesitation in her voice.
Nathalie looked down at the ringbox she'd protected for nearly 10 years and she placed it on Adrien's desk.
"This is something left behind by your mother. Take good care of it," she said and walked out.
Adrien opened a video file on his computer before looking down at the velvet box. As the video of Lorraine playing with a young him at the beach began to play, he opened the ringbox. Inside was a silver ring with a circle feature that he vaguely remembered belonging to his mother. Adrien looked at the computer screen and paused it on a frame of his mother. The ring he now held in his hands was hanging on a chain around her neck. He smiled sadly at the faint memory and put the ring on...