Honestly, I'd be more interested in finding out about what happened after she accidentally ended up in Of Noble Purpose. She seemed to have gotten there rather early on, going by Kotone's reaction. I mean, imagine if she got there before Aizen had actually started his plan, and ended up working with him from the beginning.
Well, if we roll with the scenario as presented?...Hrrrm.
Hard to call that one. I think Nemo would probably get several Captains dropping in on her and killing her.
If it somehow came down to Kotone needing to face Nemo in some way? No offense to Kotone but at the time of that Omake I don't think she had the 'absorb foreign kido for power' trick she demonstrated versus Neliel, and thus would just eat a few balas to the face before Nemo flees, not being anywhere near mobile enough to avoid getting hit.
Another problem is that Nemo kind of counters Kotone- between the sneakiness that she expresses her Reiatsu control through, Nemo holding the mobility advantage by a longshot, and Kotone's own lack of Combat skills, I'd think Kotone basically gets maybe one or two spells off, loses track of Nemo, and then the arrancar can sneak right up on the ninja wizard and shank her up close. Or prep a Cero that fries Kotone.
With the absorbing kido trick...Well, it's iffy. A power-surge doesn't necessarily deal with the idea of Nemo using Triste to create fog illusions or any other means of breaking contact with Kotone that gives her an opening to escape, and if Nemo for whatever reason goes straight for the sword fighting I think Kotone still loses, if only because Nemo's probably durable enough that she can trade hits with Kotone and come out on top that way.
Hilariously enough, Kotone I think could answer Makoto's combat style if it weren't for the massive power-gap, if that one time Makoto got Momo'd in the face was any indication.
Long term, I kind of like the way it all works out though: Makoto is too Awesome a fighter for Nemo to deal with.
Nemo hides in the shadows until she pops out and stabs Kotone.
And Kotone can use her Kido to bind and seal Makoto in place before raining down the wrath of Soul Society on the traitor Makoto.
Sword beats Sneak, Sneak beats Spells, Spells beats Sword!
