You and nanami didn't talk for days because Nanami didn't bought you the plushies you want.. he saw you're being childish so he didn't have a problem because he knew you would come back and talk in the end

You were so annoyed of Nanami.. you decided to do something that will annoy him more.. you put on a fake hickey to make a prank on him

Nanami came back from a hang out with gojo because he forced him.. you were sitting on the couch and nanami came and sat besides you.. he then noticed the hickey so he got angry as he held you from your shoulders tightly

"Who did this to you??!! TELL ME WHO GAVE YOU THAT THING?? WHO DARES TO PUT A MARK ON SOMETHING I OWN??"