Detective Pikachu was announced back in 2013, but was seemingly swept under the rug, until a trailer re-announced its existence.
“To celebrate its 20th anniversary, the Pokémon Company and Nintendo bring a new game from the Pokémon series where in Pikachu becomes a detective. Game developer shared the characters and gameplay as well as the debut date of the newest game.” stated lawyerherald.com
According to idigitaltimes.com, “Detective Pikachu takes place in Rhyme City and you’ll play as the human character, Tim Goodman who has come to the city for a currently unknown reason. When he meets with Pikachu, the story begins.”
serebii.net reported that Detective Pikachu will require 800MB of space (6,400 blocks) to download and is listed on the official Pokémon website as “Cinematic Adventure Game”, and the official Nintendo site having also listed it as a puzzle solving Cinematic Adventure.
You can watch the trailer here youtube.com. The video is provided by Japan’s Pokémon channel.