Otousan

When four-year-old Kun meets his new baby sister, his world is turned upside down. Named Mirai (meaning "future"), the baby quickly wins the hearts of Kun's entire family. As his mother returns to work, and his father struggles to run the household, Kun becomes increasingly jealous of baby Mirai... until one day he storms off into the garden, where he encounters strange guests…

In a world where people have supernatural creatures as pets, a certain family has a pet demon―Lord Satan. The main caretaker of Satan is the son, Yuuhei. From initially coaxing the new Satan out of his pet-carrier, to walking him, playing with his ball, and keeping him from fighting with the neighbor's pet Hero, this is the comedic story of a boy and his Satan.