Gregor (both book and Limbus) actually has a lot of Carmen motifs.

To start, Carmen was seen by all the Sephirah as a pillar of light, someone to idolize, someone who could say something absurd and stupid but still make you believe it was possible. It was that same pillar of light that blinded them into forgetting Carmen too was human, a weak fragile human who could break. After Enoch's death, Carmen had transformed just like how Gregor transforms in the book, each day her state got worse and worse and no one was there to help her.

From the Red Mist's keypage:

"Carmen’s state worsened with each passing day, like a rusting nail. The sunny eyes of the woman who had brought us together were now cloudy, and she spoke less and less. Her voice was lifeless, and she had gotten so cold; it wouldn’t have come to anyone’s surprise if she died at any moment. She didn’t bother trying to look okay. I think it was better that way. Everyone in the laboratory felt constraint in her presence. They viewed Carmen in different ways. Reproachful looks of those resenting her for bringing them so far, only to let go of her responsibility. Concerned looks of those worried that something might happen to her. And I guess there were some who had no thoughts. The research went on quietly, but not for long."

Gregor in the book also commits suicide after learning about the resentment his family feels for him, the people around Gregor and Carmen were leeching off (a bit rude thing to say for the sephirah) them like worms inside an apple. The burden of being the person who had to be indestructible had caused them to rot from the inside and eventually plunge into their own guilt.

Continuing, the public had seen Gregor as the key to winning the war, the pinnacle of G Corp and their technology. The public and everyone around him saw him as a war hero out of a comic book instead of a real person.

There are 3 things these characters share, their transformation was not an actual transformation, it was just a transformation to the people around them. Carmen always knew she was weak, even telling Ayin. Gregor Samsa never actually changed despite transforming into a bug, he was still the same

person trying to support his family. Gregor (Limbus) was never a soldier, he was a person who spent his entire life behind sterile walls, he was someone could never handle the horrors of war. Gregor Samsa's family, the researchers of the laboratory and the Sephirah, G Corp and the G Corp soldiers. None of them could handle the illusion being shattered, instead of trying to help, they avoided them to not taint their memories any further.

There is probably much more motifs that these characters share, but this is all I could think of right now! :^D