The basic idea is that the protagonist wakes up in an unfamiliar bed and figures out he has reincarnated into another world from the memories of the previous owner of the body.
Rank 1 Beasts have the intelligence of dogs so they can only understand basic commands, but when contracted with a cultivator can have the same intelligence as humans
Rank 2 beasts are as intelligent as humans in the wild. When contracted they are as smart as a rank 3.