Just expanding further. As Nas said, it's hard but not impossible.
Air throw isn't that great here or well....at least against rushdown Arakunes and you should rarely use it against the rushdown types. Reason for this is because of Arakune's bird aka j.6B and I think j.6C as well. I've tried air throws and they don't particularly work at least against the Arakune I play. Though, if you do anticipate the bird, you can 6A that into a free combo.
As Nas said, mix up is 6B/2B. If you jump in, watch out for the tongue attack. Slower than Noel's and Ragna's 6A but has the same property of upper body invincibility.
I'm pretty sure there are no unblockable bugs if you're in the air. You have to watch out for the D version of the bug though. It does a TON of damage.
If you're cursed and you're playing against a rushdown Arakune, wait for an opportunity to poke with 5A or 2A to get out of the curse. If it's a zoning arakune, best thing I can think of is to wait it out.
Btw Nas, if Arakune anticipates you jumping, he can do a combo leading into a curse anyways. And jump cancel which overhead? Arakune has 2 overheads he can do.
Arakune's mix ups from what I've seen so far is the arm overhead on the first hit on wake up or arakune's 2A.
A few more tips I have would be:
1. Stay out of the corner because Arakune has a corner trap that you can't get out of.
2. If you're not cursed and Arakune is doing his 2D (spitting out worm balls), Noel's 2D goes over it and will hit Arakune for you to do a free combo.
3. If you're cursed and Arakune throws you, you will be uncursed if you are able to escape the throw.
4. If you're cursed and you throw Arakune, you will be uncursed no matter if Arakune escapes the throw or not.
5. Try and avoid the cloud if possible.
Btw, I've been playing against Arakune a lot. But I've only played against 1 person that plays a rushdown Arakune. It can be frustrating at times but hang in there.