Another plot device could be the search for a lost or stolen fin - related item. Maybe it's a magical scale from their fin that has special powers. This would send the character on a quest, encountering various allies and enemies along the way.
In fantasy fiction, characters with unique traits like fins can be forgiven or accepted through the power of empathy. Other characters might learn about their different cultures or the reasons behind their physical features. For example, if a mermaid with fins enters a human - dominated world, she could show her kind heart and good intentions, which would make the humans more likely to accept her.
I'm sorry, I'm not familiar with the author of this particular novel. You could try searching for it on book - related websites or asking in a local bookstore. They may be able to help you find out who wrote it.
I'm not sure exactly as I haven't read it. But it might be about a person or a situation that has a strong hold or 'grip' on something. Maybe it's about a character being in the grip of an emotion like fear or love.
I'm not sure specifically as I haven't read it. But generally, a novel could be about a variety of things like relationships, a journey, or a personal struggle.
In Monster Hunter Stories, the cephalos usually has a certain number of fins. This could be around two or three, but it might change based on different game settings or updates.
She could use her brute strength enhanced by chakra to try and break free. If she can concentrate enough chakra to her limbs, she might be able to overpower Itachi's hold for a moment and create an opening to escape.