i use only ice magic and vitamins, energy drinks, rations
The cons of using magic is your vitality being consumed faster, while Arachne can suck part of it with her attacks (so rations are needed).
I'll suggest the following strategy. Although I did it with Compendium bonuses, it could be possible to repeat on first run:
- Physical upgrades: Max Agility and Vitality (the last one if you can). If you have SP to spare, spend it on Will.
- Weapon: Rebellion is great since you can use ice magic bullets and won't waste turns reloading it. Modded assault rifle can make it, but you need ice shells and reload after each shot. Second hand is irrelevant.
- Magic: This is the most important part. As
Crazycarzom said Cool Calm is obligatory, but I recommend just unlock it (not upgrade it, but I'm not sure if probability is affected). If you can, unlock Hell Break (Max both Fire magic and Boost attack to unlock it), because it regenerates you will and vit each turn and avoid will and vit negative status. This will consume most of your sp points, but it's worth it. If you have SP to spare, spend it on Sylph Storm (Max it if not having Hell Break).
- Accessories: Cat bell is recommended, but if you already have Hell Break then use Fluffy Coat or it's upgrades.
- Strategy 1 (having Hell Break): Do this in sequence: Cool Calm, Hell Break, Sylph Storm, proceed to attack until Cool Calm is off, then repeat. If caugh in her web, struggle until being free and avoid her attacks until she enters combat stance. Then repeat sequence. Keep an eye on your lust.
- Strategy 2 (not having Hell Break): Do this in sequence: Cool Calm, Sylph Storm, proceed to attack and recover Vitality with rations before Cool Calm is off. Keep an eye on tuns passed since activation of skills as well as your Vitality and lust (a bad scenario is you having no Vitality and your skills off).
Also, pray RNG is on your side. I hope this helps you in that fight.