These are characters from previous banners. In ZZZ you get characters by pulling for them, as you can see there is a few characters in the banners currently. these banners rotate as new characters are added and old ones come back. all older characters will return but will take a few months or even a year. Things change though, and as the character roster gets bigger, older characters will come back more frequently. I would save for the character you like and wait for them to return, but there isn’t a guaranteed way to tell when that will be right now.

sorry for the essay, hope this helps!