Detective Pikachu seems like an ordinary Pikachu, but with some MAJOR differences: He is able to be understood (within The Hotel) and very intelligent, although at the cost of most of a normal Pikachu's electric abilities. In fact, the most power he can put out would be the equivalent a normal static shock, such as from dragging one's feet on the carpet.
He is the main Pokemon of a famous Interpol agent, Anabel, who spends her days investigating various supernatural phenomena in and around the Kanto region (a region made up of 6 prefectures including Tokyo) and is currently trying to hold down the fort while his partner's abroad tracking strange happenings involving creatures that have been dubbed the "Ultra Beasts." Detective Pikachu's current assignment is investigating a phenomenon dubbed "The Curtain of Cruelty."
While with his partners in Boston, Massachusetts, Detective Pikachu met Suu, and they struck up a friendship. As Suu was getting ready to depart for Japan, news came that Hiromi Kawanami had vanished from Ginga TV after throwing equipment around in an uncharacteristic fit of rage. Detective Pikachu realized that this was one of the Curtain of Cruelty's effects, and decided to head to Japan to check things out there. He was later joined by his owner, Anabel, and her colleague, Looker.
When speaking English, Detective Pikachu has a very strong Boston accent, and sounds somewhat like Danny DeVito.