k guys, here me out. we need a twin switcheroo event. imagine this:

Sayo gets sick but Roselia has a live show the next day and have to perform because it's really important. But how are they gonna do that without their guitarist, Sayo? They'll never be able to find a replacement in time.... But wait. Hina is a genius and since she's Sayo's sister she already knows all of Roselia's songs and with a little bit of practice she can dress up as Sayo (putting on a wig or something), and perform with Roselia. Sayo recommends her for the sake of the band, but inside she feels like maybe Roselia doesn't need her. After all Hina is just as or even better at the guitar than Sayo. A few days after the live, Sayo gets better and goes to practice with a heavy heart. Roselia then tells her how much they missed her, and everyone is happy again.