Well, I'm a rather new Valk player, but I would like to get this vs. Arakune board moving, as I have a friend that consistently gives me trouble with Arakune. I'll jot down what I've seen below, and follow up with some of my own issues and questions!
Punishes: I've had good success playing Arakune's distance game. Whenever he goes for his j.6D OR his j.236D, if I respond by jumping and w[66D] > j.5C > 3C then I am immediately in, and on the offensive, which is where Valk wants to be vs. Arakune. You can also switch up the 3C for 6C for a high-low switch-up, but the 6C is not safe.
Anti-airing: Only success I've had here is 6A, or w[5B], followed up by their respective follow-up combo's. Generally, if Arakune is in the air, I'm in the air as well because Arakune's j.66 > j.4B can beat out most of my AA attempts.
Zoning: Generally, Valk wants to be in Ara's face, not zoning. But if Arakune starts to zone you, you can run the w[66D] > j.5C > 3C (or 6C) to close the distance, as this arcs over the 6D bug and all clouds, depending on your timing.
Their game plan: Alternating between zoning / bugging / clouding you, and baiting you into AA's. Be careful when wolf cannoning in at Arakune or he will 5C you into some huge curse meter gain.
Strategy: Run different angles of attack constantly. Pressure, pressure, pressure seems to keep Arakune at bay, but don't get reckless, or you will get cursed, which is very VERY dangerous for Valk. Low health + 4 guard primers means that you need to be aware of everything Arakune can do to break your primers, and dodge them if at all possible (chicken dodge w/ barrier during curse block strings).
Obviously, any seasoned Valk player will read this and laugh at me on many points. Again, I am new to Valk, but I very much like the play-style he runs. I constantly get mixed up by Arakune's high-lows and cross-ups mid-curse block strings. Any suggestions of when I can poke Ara out of his block strings, or better ways to keep him on the defense would be greatly appreciated!