The phrase "locked characters" refers to video game characters or features that are not available or accessible until certain conditions are met or progress is made in the game. Full definition
Blackouts lock characters in rooms and turn the cards, so the power struggle between the three leads is constantly shifting. (oracleoffilm.com)
Even better, there's a weekly rotation of free trial characters — you don't need to own Nova to play Nova this week — plus playing the game awards tokens that can be used to select any other locked character from the selection screen. (kotaku.com)
Based in the SAO universe, the storyline, the SAO universe locks our character inside the virtual - reality world. (fraghero.com)