At one point in "Turning Red," Mei's mom asks her this very question, and it certainly echos viewers' thoughts as they watch the movie. Well, there's no real answer to this very valid question, unfortunately.
The number four in 4*Town could be a play on the fact that two members in the band have the same name (Aaron T. and Aaron Z.) and fans sometimes group them together ("Jesse went to art school, Tae fosters injured doves, Robiare speaks French . . . and Aaron T. and Aaron Z. are, like, really talented, too!" Mei says at one point).
It could also be the movie's creators poking fun at boy bands whose number of members don't match the number in their name. There have been quite a few throughout history. Australian boy band 5 Seconds of Summer has only four members, K-pop group Seventeen has only 13 members, and British boy band 5ive now perform with just three members. So it seems like having 4*Town have five members is left unexplained because it's meant to be inexplicable, and that's what makes it peak boy band!
