On his desk.
In his room.
'Ladybug would never approve of this,' Adrien thought to himself, eying the green-tinted glass jar wearily, but also with interest. The black butterfly had stopped flapping about and a tiny part of Adrien was afraid it may have been dead.
Adrien rested his chin on the desk's surface, allowing for his eyes to be level with the akuma. He risked tapping his nail gently against the jar and a light 'clink' broke the silence. The akuma's wings closed then opened again, indicating that it was indeed still alive.
"Adrien, get rid of it!"
"Why? It's not like it's doing anything in that jar!"
"Not yet, it's not. But for for all you know this could just be some sick and twisted trick."
"It's a butterfly, Plagg. It doesn't have anything planned."
"But Hawkmoth definitely does! I say you transform and destroy it right now and we can forget this whole debacle ever happened!"
"Wow, something really must be up if you're willing to transform."
"Something is up! My holder is keeping an akuma as a pet in a jar!" Plagg huffed.
"I'm just observing it! Nothing wrong with that!"
"Hawkmoth could be using it to spy on you or something!"
"Did you and Milady switch bodies while I wasn't looking?"
"Adrien! Seriously! Keeping that akuma could put your secret identity in jeprody."
"If Hawkmoth knew my identity, he would have likely come bursting through the wall right now."
"Fair point. But I still say this is a bad idea!"
"Says the guy who sunk Alantis."
"I told you, that was an accident!"
"'It was in my way' is not a valid reason for that kind of accident."
"Stop changing the subject, Adrien! There's no way you'd be able to keep your secret identity intact if you keep that thing around!"
Adrien huffed, placing his hands on his hips. "I guess we'll just have to agree to disagree."
Plagg glared daggers at his holder. "I'll destroy it! I will."
Adrien's eyes widen in alarm. "Don't you dare!" He scolds the black kwami. "Ladybug isn't here to fix it!"
"Cata-!"
"Plagg, claws out!" Adrien interrupts Plagg and the mini god of destruction is pulled into the Miraculous against his will.