Note: I had the community patch and balance polish mod installed (in case that affects some of the interactions of abilities).
I modded Rekke's class/subclass choices for this build. These two subclasses play nicely with each other and have a good amount of synergy. The Helwalker side gives us some nice buffs in the form of Swift Strikes (for faster action speed), Clarity of Agony to reduce hostile effect duration, and most especially +10 Int and +10 Might from the Helwalker trait and Duality of Mortal Presence. Enduring Dance can quickly get you to 10 wounds for that +10 Int/Might. The main drawback of Helwalker is that you take a lot more damage.
On the Fury side you get bonuses to Elemental keyword spells (penetration and range) and a special shifted form at the cost of not being able to cast Restoration spells. You're essentially encouraged to cast from afar (which plays into staying out of danger lest the Helwalker drawback get you killed) and cast damaging Elemental spells with increased pen, AoE size from the Helwalker Int, and damage from the Helwalker might.
In most fights you get to stand in the back and just unleash on the enemies. You sometimes want to get a tad closer for Relentless or Returning Storm to be able to hit but even then the AoE size is pretty decently large. If an enemy happens to get close enough to attack you, your shifted form has a fast-cast teleport spell to bail you out and reposition yourself.
The biggest drawback to this build is probably not getting access to the last two Druid power level spells for Great Maelstrom and Avenging Storm. However, both of these spells exist as scrolls so investing in Arcana can alleviate this issue. There's also the helm Heaven's Cacophony which gives you a per-rest cast of Avenging Storm. Avenging Storm is nice when combined with the Fury's shifted form which has a bounce to its attack, giving you multiple lightning strikes per attack when you don't want to cast any more big Elemental spells.
I happen to not like using consumables very much, though, so I didn't often use Maelstrom/Avenging with Rekke. Absent those spells he felt somewhat less impactful. Relentless/Returning Storm have nice stuns but its random and therefore less reliable. Spells like Hail Storm or World's Maw were nice, especially with the humongous AoE size but their damage was often underwhelming compared to the AoE from my MC as an Arcane Archer. I think I expected this glass cannon to have a bit more cannon (he certainly had the glass part down when at 10 wounds 😅).