She's a 『Mob』.

However in her own story, wouldn't she be a 『heroine』 instead?

A story about a girl who had a rather unique magic and with that magic, she has an ability to create a link from her world to another world. Using that magic, she somehow stumbled upon a creature called 『tablet』 which inside it was an otome game called 「Otouto's Affection」.

As she played that game, she realized that her world was the same one with the world inside the game and she had a role inside the game which is a mob. Thus, as a romance story lover — she claimed it herself — she was determined to watch the romance unfolded with her own eyes.