Having ur party with 10k+ hp and a Sentinel might help, dont think it does more than 10k dmg :o I'm not sure if if physical or magic resistance would help, think that needs testing :) I was only able to defeat it cos I was rather lucky with gettin an instant stagger and killing it before it had a chance to do Screech :o
sen/sen/sen wouldn't do any damage, and I only have the basic roles. lightning's hp is like 7.5k and sazh (random instant stagger) and vanille's (death) are even lower, so their techniques don't really work well, especially against screech. I've put on the 15% magic resist and they didn't seem to help, only survived when I had 2/3 accessories as +500 hp.
http://www.last.fm/user/xvsanx lettin' out a chest full of reeeefer, askin' adversaries 'do u want sum eeether?'
As someone who refuses to ever grind, use guides or use cheap tactics like Instant Stagger(Because I don't read about the game online I don't even know how to get that ability), this is how I beat Neochu:
By using Death(cheap tactic).
Sorry, that thing is near impossible to beat by conventional means unless you either level up or go cheap. Surviving screech is pretty easy, just go SEN-SEN-SEN and stack up defensive accessories, but it follows up Screech with Pollen, which puts almost every single status ailment on all your characters and removes all their buffs. It's just impossible to recover fully from that before it hits you with Screech again.
I tried for a while though, and probably got it down to 3/4 of its health, but from its Libra description it seems it'll eventually summon those little Chus as well, and that makes it completely impossible.