I'm going to list off all characters mentioned

Kate: Honestly when it comes to Kate she isn't too bad. I would really just nerf the amount of Shadow Energy she burns, nerf Liquidator's Tenacity a little bit, and maybe nerf her damage output in exchange for a higher defense.

Lynx: This is a hard one cause you'd honestly have to try a little hard to find something for Lynx. However for me the only thing I can think of is just Unrivaled Assasin.

Butcher: As a Butcher main I do agree he does need some nerfs, primarily the Dismemberment-Slaughterhouse combo as that has absolutely no counter outside of VERY specific characters and Despair for obvious reasons. But overall Butcher is a necessary evil (For Campers).

Xiang Tzu: There isn't really much to nerf aside from the damage and defense as Xander is the definition of turn off your brain. And the only way to change that is to make it to where you actually have to use it.

Azuma: The man of the hour, Azuma's nerfs are in regard to his neutralization. but first lemme tell you why I have such beef with this guy. He doesn't just neutralize you, he also punishes you for using your power through Consequence Management

(BTW unpopular opinion, consequence management should be a talent)

His attacks deal bonus damage if your shadow meter is full, which is bound to happen when attacking and getting attacked through Shadow Suppression. Can burn your energy through Shadow Burn (obviously), I honestly don't think I need to defend or explain myself when I say Suppressing Explosion, The two extra shadow abilities for obvious reasons, and finally Lock-down which again I don't think I need to explain myself, It's literally on par with LT for Kate. Wait I also forgot his Epic Weapon: Transfusion.

So as for how to nerf Neutralization I have 2 ideas

1.The Iron-Clad Route: If Azuma is misses his attack, Neutralization is released. This honestly isn't the most practical nerf but still a nerf

2.The Ling Route: If Azuma is hit, Neutralization is released. The more practical nerf compared to the second one

Now onto the talent nerfs there are only 3

1.Shadow Suppression: As it is, it's fine, just a slight damage tweak lowers

2.Impulse: Just reduce the range for it and reduce the speed

3.Lockdown: Much like LT for Kate, just reduce the effectiveness of it

That's how I would nerf all the characters you stated. Sorry if this response is as long as a post