The plot of Hogwarts Legacy was purposefully set in a time period where many pre-established characters from the Harry Potter franchise (such as Newton Scamander or Harry Potter himself) are not around. According to lead writer Moira Squier, this was done in order to provide the player with a unique world. As part of this, the writing team focused on creating a diverse collection of characters for players to potentially identify with:


However, while main characters from across the franchise are not present, selected minor characters (such as Nearly Headless Nick and Peeves the Poltergeist) are still present in the game.

Hogwarts Legacy is notable for introducing the first transgender character in the Harry Potter franchise in the form of Sirona Ryan, the owner of the Three Broomsticks pub who outright tells the player that it took her classmates "a second to realize I was actually a witch, not a wizard". This drew attention as the creator of the Harry Potter franchise, J.K. Rowling, has generated controversy over the years by making comments that many have criticized as transphobic. It is worth noting that while she would receive profits from the game's sales leading many fans to boycott the game, she had no involvement in its development. In regards to the inclusion, the developers stated:


However, after the character was revealed, several fans further complained that the name Sirona Ryan rendered the inclusion of a transgender character tone deaf and continued promoting the boycott. The name "Sirona" originates from the Celtic goddess of healing and rebirth and is symbolized with imagery of snakes (animals that shed their skin) and eggs (where many birds, fish and reptiles among other animals emerge from after incubating). Despite being a feminine name, they claimed to perceive it as a male-presenting name due to that variant of the name containing and potentially being shortened to "Sir", while also pointing out that the surname "Ryan" was a masculine name and an anglicized form that was used instead of the less common authentic Gaelic name "Riain". This set up the name to appear as an unintentional pun: "Sir Ryan". Despite these complaints, the boycott turned out to be a failure as Hogwarts Legacy became commercially successful, selling over 12 million copies in its first two weeks of release and going on to sell double that amount by the end of 2023.