Hello there. Okay yeah I’m a pretty big fan of the show.
Firstly. Technically Master Fu would be the guardian of the cat miraculous since he is the guardian of all the miraculous (Not gonna spoil anything from the latest season) But Also Adrien Agreste would be the guardian since he is the holder of the miraculous.
As I said above the guardian of the miracle box would be Master Fu. (Again not gonna spoil anything)
The answer is the first 1
"That" is the relative pronoun because it refers to People, Animal, and Things, defining only.
Explanation:
I hope this helps for you