Basically character one needs a place to stay, for a reason that can be decided by the writer, and character two is a lonely person who decides character one can stay with them as their pet, literally. A line similar to the set up of the drama Kimi wa Petto. You don't need to have seen the drama though.
Could be slash, femme, or het. And I'm leaning more towards playing the pet, but could play the other character. Plus there's more in the journal, including PBs I like to use.