She knew already.

"Now Marinette, I know this might seem strange, but can you hear me out?" Kagami asked.

Marinette crossed her arms.

"Where's that dress that I made extra special for you?"

Kagami averted her eyes. She murmured something.

"What was that?"

"...I got it dirty."

Marinette uncrossed her arms and put them on her hips, making her look more like an authoritative mother that caught their child in the middle of doing something bad. Then she went from giving her a glare to a cheeky smile.

"That's alright 'Gami. Babies make messes all of the time, and you're just my wittle baby girl."

Marinette picked a chair in the room and sat in it, patting her lap. Kagami took this as permission to sit in her lap, her cheeks still blushing. Marinette bounced Kagami on her knee, thought their similarities in weight and height only rocked Kagami slightly.

"Is Wittle 'Gami happy to see me?"

Kagami nodded.

"Yes Kaa-san. I'm happy you're here."

When Marinette learned about Kagami's secret interest, she volunteered to not only keep it a secret, but participated too. Kagami suspected she only agreed to it so she could use her as a living model, because every time they met for their "sessions", Marinette would come with a box full of custom-made dresses and onsies and costumes. Kagami didn't mind, since they were all stylish and made her look cute and babyish.