Servamp
So I saw something similar to this in a fic before (don't remember which), but the Eves forget their Servamps. (This takes place before Wrath and Gluttony find their Eves so just the five pairs for now)
Like, something happens which causes them to get amnesia and forget they ever even met their servamps, and obviously the vampires are upset.
Kuro doesn't have Mahiru nagging him anymore, Hyde doesn't have Licht yelling at him, Lily doesn't have Misono to care for, Jeje doesn't have Mikuni to demand for blood anymore, Hugh doesn't have Tetsu to entertain him anymore, etc.
Obviously they are lost without Eves, and Hyde and Hugh are constantly whining and crying (because they're definitely the type).
All the Servamps are depressed, meanwhile the Eves feel like they are missing something, but can't figure out what.
Since they don't remember their Servamps, they also don't remember each other, and even Kranz and the others and everybody they know are wondering where their Servamps are and why the Eves can't remember them.
The Eves can't figure out for the life of them why everyone they know are asking about these people they've never even heard of before, and why everyone seems to know who they are except the Eves themselves.
Meanwhile, the Servamps are hiding with their other siblings as they grow tired and weak with the distance from their Eves, desperately attempting to follow them without being noticed.
Eventually, the Eves notice they keep seeing the same animals or people nearly everywhere they go, and grow agitated or confused.
Kuro often stays a cat and pretends to be a stray so Mahiru doesn't get suspicious.
Jeje hides in the grass as a snake to seem less stalker-ish (because being tall and always wearing bags on his head? he defo looks suspicious) and to avoid being seen by Mikuni.
Lily flies as a butterfly and just lands in a random place to watch over Misono.
Hugh and Hyde are a bat and a hedgehog, which aren’t seen roaming around in the city much, so it would be weird for them to be seen in daylight often unless they were looking to find new Eves, which they aren’t. So they can't really go to see their Eves in the daytime.
For Hugh, it’s still difficult because he looks like a child, but for Hyde it’s easier for him to navigate as a human, although he can’t let himself be noticed. Kranz and the others, who do recognize and remember him though, pretend not to see him and act as if he isn’t there, so as to let him roam near Licht more freely, although they do question why Licht can’t seem to remember him.
The others try their hardest to get the Eves to remember the Servamps, though for the life of them the Eves can’t seem to remember them at all.
The Servamps grow weaker as it gets harder to keep up with and follow their Eves, until eventually they grow too weak to move.
The Servamps grow closer to dying.
Eventually, the Eves do finally remember their Servamps, and try desperately to find them, to no avail.
Until one day, they bump into The Mother, and she leads them to where their Servamps are.
The Eves take their vampires home and try to nurse them back to health as much as they can, and some may not admit it, but they’re worried sick about the Servamps.
Eventually, the Servamps get better, and a lot of fluff happens.
Then, all is good!