What new player-character option did Pokémon Crystal introduce?

Pokémon Crystal introduced the option to play as a female protagonist.

Released for the Game Boy Color, Pokémon Crystal was an enhanced version of Pokémon Gold and Silver. It retained the Johto region and the core story while adding new scenes, animated battle sprites, a Battle Tower, and other improvements.

Earlier main-series Pokémon games gave players a boy protagonist by default. Crystal was the first Pokémon role-playing game to let players choose a girl as the playable character. The selected character does not change the game's main objective, but it changes the player's appearance and some dialogue.

This feature is sometimes confused with the female rival or with later character-customization systems. Crystal offered a choice between two fixed protagonist designs; extensive outfit and appearance customization came much later. The game was also notable for making Suicune more prominent in its story, although the female protagonist option is one of its most important lasting additions.