She was alone and planned to live for herself, but unexpectedly crashed into another "world"
He has lived alone in the world for thousands of years, drinking the same cup of tea day after day and watching the reincarnation of the world
One is her, one is him, one is an old ghost and the other is a cat. Destiny makes them meet after all.
It's good to have "someone" by your side to survive in this fucked up world.