Hi Kassandra,
I’ve moved this post to the bonding section, where it might get more input.
Agree with Sarah, separate, neuter, and let hormones settle (and let them forget about the fight). One scuffle will not make a bond impossible, and after neutering he will smell different, so hopefully Sushi won’t even recognize him .
I made a similar mistake with my first pair, when I had no idea what I was doing really (aside from reading some articles online). Both were neutered/spayed, but after their first date in the tub (which went really well), we decided (dumbly) to let them interact in the main room. Bam, fighting happened! I eventually bonded them though (the pair in my avatar). So don’t lose hope!
The bathroom and bathtub sounds like a good starting spot as neutral. You might also reach out to friends to see if you could set up a pen in their kitchen or garage for if you need more space or need to change things up.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.