Brainrot
Brainrot is a word that some might use when referring to constantly thinking about a topic, person, place, or thing. It's a spoof word that's relatively close to the definition of a hyperfixation. Both words stand for the same meaning, however, brainrot isn't meant to be taken as literally. There aren't any brains rotting, here!
Example:
Person 1: Hey, man. Are you alright? You've been going on about Gon Freecss for a while, now..
Person 2: I'm alright! I just have a case of brainrot, is all. NE, NE KILLUA!
Person 1: Hey, man. Are you alright? You've been going on about Gon Freecss for a while, now..
Person 2: I'm alright! I just have a case of brainrot, is all. NE, NE KILLUA!