This is the second-in-command, cross-eyed character. She is not the heroine.

I possessed the 5-star character Lucia from a gacha game. She was a test subject for an organization, and she wears a leotard, swings a katana, and sweeps away enemies...an ordinary, cross-eyed character. [The protagonist gave you the Ring of Oath!] No. I told you I'm not the heroine.