This can absolutely be about the other bunny in the the house. Rabbits have a very keen sense of smell. Kovu could have picked up the scent from your clothes or skin. Rabbits are highly territorial.

Hopefully he will calm down soon, when he gets used to the scent of the other bun. What are your plans for the new bun?

If the bunny is still a baby, I would keep them separated. Letting them interact young isn’t really beneficial for either, especially once baby bunny starts bunny puberty and hormone levels get high. After the new bunny is fixed, it’s good to start pre bonding for a while before starting full-on bonding sessions,

Do you know how many weeks old your other rabbit it? In short, if he/she is less than 6-8 weeks old, it is concerning that they are separated from their mother at this time and will need a different diet.

As Louie mentioned, they should be kept separate, especially if there was aggression. There is little to no benefit for trying to do dates or interactions between them because the younger rabbit will go through puberty in a few months and this will most likely change the entire relationship dynamic, whether it is super cuddly or super aggressive. Both rabbits should be housed separately for safety reasons as well, so separate areas and no shared wall (in case Kovu bites through the cage). After the younger rabbit is fixed, then the bondig process may begin.

It is important for her to be eating pellets at this point because she is growing and needs those nutrients. Are you offering alfalfa-based pellets? Those tend to be very popular with rabbits.