Well, often he has to figure out how to communicate. He might try to use his body language in creative ways to get his friends' attention. For instance, he could lead them to where danger is by pawing at their feet and then running in the direction they need to go.
In such a fanfiction, a lot could unfold. Elena might face conflicts with other supernatural beings or have internal battles with her morality as a vampire. Also, there could be romantic complications with the people in her life.
Well, she has all kinds of adventures and discovers a whole new world from a cat's perspective.
Maybe in this fanfiction, Midoriya as a girl discovers new aspects of her power. Since her body has changed, the way she channels her quirk might also be different. She could then have to train all over again to master this new way of using her ability.
Well, she might face discrimination at first. People in the hero world could have different expectations of a female hero. Midoriya, now as a girl, would have to break through these stereotypes and prove herself just as capable as she was before.
Well, in the fanfiction, Harry might first try to find the owner of the cat. He could use magic to see if there are any identification spells on the cat. Then, he might take it to Hogwarts. The cat could be a magical cat with special abilities, like being able to talk or lead Harry to a hidden place in the school.
It might cause a conflict within the Akatsuki as some members have different views on Sasori's actions. Or it could be the start of a series of strategic battles to defeat Sasori and restore Sakura to normal.
One great fanfiction with this premise could be 'Midoriya's Feline Adventure'. In it, Midoriya's transformation into a cat brings out some really cute and funny situations. His friends initially don't recognize him, and there are a lot of misunderstandings that lead to comical scenes. For example, Bakugo tries to shoo him away thinking he's just a stray cat, not realizing it's Midoriya.
Well, usually it leads to all sorts of adventures and challenges. Harry might struggle to adapt to his smaller size and less magical abilities.
One idea could be that Batman is turned into a cat by a villain's new experimental device. As a cat, he has to rely on his natural feline abilities like stealth and agility to still protect Gotham. For example, he could use his cat form to get into small spaces in buildings to gather evidence or spy on criminals.
He might explore the spaceship out of curiosity. Naruto is always eager to learn new things, so he'd be all over the controls and strange gadgets inside. He could accidentally activate something that sends out a signal, attracting either help or danger.