Answer

Hello again, and thanks for your reply, with additional information. I was not online at the time, so thank you also, for your patience.

I'm sure that Kikyo is feeling stressed by the arrival of little Noah, and you can help by 'starting over' with the introduction process, as outlined here:

http://www.howardcountycatclub.org/introducingcats.html
http://www.pawschicago.org/PetCare/catintroductions.htm

It's always best to not rush the introductions, and introduce the existing cat to the new arrival's scent by taking a slightly damp cloth or paper towel and petting Kikyo, then Noah, then vice versa, frequently, throughout the day. Noah should be kept in his own room with food, water, litter, toys, scratching post, bed, etc., and Kikyo should be allowed to sniff him under the door, then after a few days, you can let her see him through a crack in the door, and then you can supervise their face to face meeting, and offer healthy cat treats and 'interactive' play with something like a laser pointer. Some initial hissing, growling and swatting by Kikyo is to be expected. That's totally normal and based on instinct. A new 'creature' has invaded her territory, and she doesn't want to have to share YOU, either!

Your kitties might benefit from a cat appeasing pheromone called Feliway/Comfort Zone for Cats, which comes in both a spray and plug-in diffuser. It's available at major pet supply stores, and also online. The diffuser resembles a plug-in air freshener, but has no scent to humans. Feliway helps to relax stressed or anxious cats, and is useful in a multitude of situations, especially new introductions. For more information, please see: www.catfaeries.com/feliway.html

If Kikyo had changed to become more territorially aggressive, since she was a kitten, this may have been sparked by a startling/frightening occurrence, of which you were not aware, or she may be in discomfort from an underlying medical condition, so it's always a good idea to have her evaluated by her vet, to make sure all is well, physically. With the introduction of Noah, she was further stressed, but once they become friends, I think she'll appreciate the company.

I'm glad you're already keeping him semi-isolated, so she can't harm him due to the difference in size. Once he's full grown, he might be bigger than she, because males usually grow bigger, in general. It's great that you plan on neutering him at about 4 months; you're a very responsible cat-parent!

Try some of these suggestions, and I hope they eventually get along. When you introduce new cats to each other, they may never be 'best friends', but if they 'tolerate' each other, that would be fine!

It would be a shame to have to re-home Kikyo, but if you feel, after a good while, that she is just too aggressive with Noah, and you, she might be better in a single cat household. If it comes down to that, ask some cat rescue organizations in your area for help in re-homing her.

I hope everything works out for your two furbabies!

Cher