Senzawa should honestly just come back as Sen instead of being Saba. She could still make Sen have an ocean theme by making her a sailor girl who went out to sea to "find herself" or some retarded first world white girl bs like that.
I'm not saying fuck Saba, I'm really excited for Saba to (hopefully) debut, but if I had a gun with one bullet and was forced to shoot either Sen, Gura or Saba, then I would likely shoot Saba.