Currently, the only filtering options for friends regarding Rebirth are "None", "Unlocked" (have Rebirthed), "Locked" (isn't Rebirthed or Rebirth unavailable), or "Anima" (I think only shows friends with Anima selected as their portrait?).
These options aren't necessarily intuitive at first glance, and they could be more useful. For example, it's currently not possible to find units that you haven't Rebirthed but have the option available to them without putting on "Locked", sorting by Universe and manually clicking through every single unit to look for the Rebirth symbol in the top left corner. This is just frustrating for someone like me who sometimes takes breaks from the game, and would likely be frustrating for someone who has lots of units and wants to focus their time and energy on a select few.
I'd suggest splitting them up into "None", "Has Rebirthed", "Rebirth Ready", "Rebirth Available", "Unavailable", and "Anima". Obviously the names can be shortened or changed a bit, but should still carry these general definitions so that someone can understand them at a glance.
#Finer filtering for friends in regards to Rebirth status
vital dune
frozen sparrow
I would love to add wedding dress locked unlocked to what you say cause i wanna be able to see in the same screen all the units that im missing the ring costume so i can decide who gets it next