Detective Pikachu didn't exactly set itself up for a sequel, but there is a way Detective Pikachu 2 could happen with Ryan Reynolds returning to add his comedic vocal tones to the titular mouse Pokémon. Even before Detective Pikachu hit theaters, there were rumblings that a sequel was in the works, and this prospect looks even more likely since Detective Pikachu ultimately went on to become the first truly successful video game movie. Prompting an enthusiastic response from both critics and Pokémon fans, Detective Pikachu also flourished at the box office, narrowly losing out to Warcraft for the title of highest-grossing video game movie in cinema history.
Much of the discussion surrounding a potential Detective Pikachu 2 has focused on a shared Pokémon universe approach, rather than a direct sequel, with the next film telling a completely different story within the same Pokémon world. This seems the most likely option primarily because Detective Pikachu's ending wrote itself into a corner with regards to any future installments. After Justice Smith's Tim Goodman spent the entire film bonding with his new-found talking Pikachu, he eventually discovered that the personality inside the Pokémon was that of his missing father and, by the time the end credits rolled, normal service has been resumed, with Tim's Dad back into his usual Ryan Reynolds-shaped body and Pikachu reduced to a regular Pokemon that can only utter his own name.
While Detective Pikachu had many points of merit, the movie's biggest draw was undoubtedly Ryan Reynolds voicing a snarky and caffeine-addicted Pikachu, and any sequel without that character risks pushing away a section of the first film's audience. Detective Pikachu 2 with a regular Pikachu, unable to make jokes and hurl insults, just doesn't have quite the same appeal. The obvious solution is to engineer a story where Tim's father has to put himself back into the body of his Pokémon pal. Detective Pikachu established that the technology to transfer a human mind into a Pokémon body does exist and Mewtwo's psychic abilities are able to perform the same trick. It wouldn't be too far of a stretch for Reynolds' cop character to come across a case that he simply can't solve without being 2-feet tall and covered in fur. However, this solution presents its own set of problems.
Detective Pikachu showcased a wonderful dynamic of friendship between Tim and Pikachu, before the duo realized they were actually related. Should these same characters set out as father and son in Detective Pikachu 2, their relationship would not only be completely changed, but would represent a massive departure for the Pokémon franchise in general. The comedy value in having a Pokémon as a parent would wear off rapidly and the core franchise message of setting out on a journey with your best friend would turn into something considerably less fun. The solution is to have Ryan Reynolds' Pikachu go on an adventure with a brand new human partner in Detective Pikachu 2.
Admittedly, this is somewhat harsh on Justice Smith. The actor did an admirable job of playing the lead human protagonist in the first Detective Pikachu and his character still has room to develop further. For obvious reasons, however, Tim Goodman is not as vital to the success of Detective Pikachu 2 as Pikachu himself. If Tim's Dad is forced to once again transfer into Pikachu's physical body to investigate a case, he could potentially partner up with Kathryn Newton's reporter character from the first film or a rookie cop partner working on his first real job. This would allow the Ryan Reynolds version of Pikachu to once again lead the movie, but without falling into a strange Pika-parenting scenario.
Given Detective Pikachu's box office success, a sequel of some kind feels inevitable and bringing back Ryan Reynolds is smart from a financial perspective. Reuniting Pikachu with Reynolds' wit may not be straightforward, but bringing in a new human protagonist would preserve all the strongest parts of the first Detective Pikachu, while adding a fresh face to the sequel.