I'm so excited for this new development, I actually quietly screaming "AWESOME!" after the chapter LOL. I always thought it'd be nice in these isekai stories to have another person they know come over too (mind you having one isekai journey is improbable enough much less two to the same world and time period but lets ignore that 😉). Moreover, I think this is the friend she mentions in the flashbacks who was further along in the game so she'll definitely be able to help if she remembers the secret character again. Who am I kidding of course she'll remember, but the question is how long it'll take for Katarina and Sophie to recognize each other for their past selves (my bet is Sophie puts it together first since we all know Katarina is as dense as a rock).