This is my favorite way to build [Xaku]. It retains his destructive capabilities while being EXTREMELY comfortable to play.

The [Primed Flow] slot is flexible and up to choice. You can put [Streamline] in if you don't have arcane energize and it will still be very comfortable. You can also put [Augur Message] in for an easier to maintain Gloom, as well as some more defense through shields. Both those substitutes also require one less forma, so very cheap and easy with similar power.

The idea of this build is to utilize Molt Augmented as your means of hitting your 200% power strength necessary for the full armor strip. This requires about 90 kills. Up to that point the 90% armor strip this comes with is plenty. Once your Molt Augmented is fully stacked your gloom, and your Grasp of [Lohk] will be incredible.

This build does hinge on having Molt Augmented. You can even do this with lower rank versions of Molt Augmented, but it requires more kills.
You could run a very similar setup as this using [Growing Power] instead of [Brief Respite], if you don't have Molt Augmented. But you will notice a significant drop in defense. It is also a bit more janky to maintain when needed.

Please enjoy my personal take on [Xaku]!