Whirl?
I base Whirl after a blue lobster.
Whirl is an artist. He's always had an artists soul and before the war he had hands to help him with his art. During the war he pissed off the wrong people with his work and he suffered gravely for it. One eye was carved out while his hands were crushed and broken. No healers could help him.
His anger became to consume him because he couldn't vent it out anymore. He sharpened his nails into claws and started to become more feral. Mers often look more human than fish but Whirl dove into his animal side and never truly recovered.
He joined the wreckers so he could destroy the people who destroyed him. However he was too violent even for them and he almost lost his sanity.
He has a strong hate for Megatron and the war. It took eveything from him. It made him this. The Lost Light Pod found him and although very redundant he did eventually join them. A small cuddlefish (Tailgate) making him feel at home and an octomer (Cyclonus) making him remember why he held on so long in the first place.
His hands can never be fixed but at the facility his claws are taken good care of and his eye wound and scars are properly medicated. He slowly with the help of his new pod (and gasp friends) learns to do art again, albeit in a different way. His work becomes quit famous and he's proud of how people oggle at it.
He loves shiny things. Hoardes them and steals from others. Shiny and pretty things. No one knows why. No one asks.
Whirls afraid to really show himself in the aquarium part of the facility so he sticks to the back. In private tanks and pools where he can be left alone.
Whirl from afar or hidden enjoys watching the kids at the facility. He likes scaring the scientists but he can never bring himself to scare the kids. He watches wishing he could tell them war stories and see their faces light up the same way Kup or anyone else can.
Some day he'll be less ashamed and more confident. He may be loud but he knows how he looks how people feel about him. But your slowly changing his mind. With how often you say you like his marking and scars. When you trace his shell his heart flutters. Maybe soon he'll feel he deserves nice things.