Hello @リサラ58322263,
Thank you for your message. I am sorry you are having this problem.
If your reference background is transparent, fill it in with a contrasting colour. If it is not transparent, ensure there is sufficient contrast in the reference image. Move the sliders all the way to the right. In your prompt, you might have to say something like, "in the shape of the character XXX".
If none of those work, please share your reference image.
Thanks,
droopy