Transmeowtation is a nen ability I dropped in a comment a couple months back, but I decided to revisit it and expand it a bit.

Transmeowtation: a transmutation ability that turns the user’s aura into a mass of nen cats surrounding the user. If the user is not activating an ability, the nen cats will behave as real cats normally would by rubbing up against the user’s legs, climbing the user or nearby structures, taking naps in sunny spots, etc. The longer the cats are left to do as they please, the less nen it requires to maintain them. The cats can use their claws and teeth to attack, clump together in soft furry masses, grab onto each other to form long chains of nen cats, and amalgamate to create large nen cats or nen cat features.

Cat fight: The mass of nen cats collectively lashes out with claws & teeth at anyone nearby that means the user harm. They do so autonomously, without needing to be directly controlled by the user, but they will not break contact with the user while doing so - severely limiting their effective range.

Fe-line: Multiple nen cats grab onto each other, forming a chain of nen cats that extends the reach of the cat mass. This must be activated by the user.

Cataclysm: The mass of nen cats amalgamates into a large, singular cat-like aura enshrouding the user. The power of this giant nen cat aura is greater than the sum of its parts, enhancing the user’s offensive and defensive abilities. It must be actively controlled by the user.

Fury of the Cat God: The nen cat aura changes, giving the user a tail, a thin coat of fur, whiskers, and pronounced cat-like claws and teeth. Much like Cataclysm, the user’s physical abilities are enhanced, with a small increase in power for every nen cat that has been defeated in battle so far. The longer this ability is active, the more cat-like things the user must do afterwards (like scratching things, eating fish, etc). If the user stay in this mode for more than 9 minutes, when they deactivate this ability they will effectively be feral for 1 hour per minute they go over.