This is a specialized build for [Ash]´s 4 (aka blade storm), an ability that scales with [Steel Charge], atack speed (capping at 50%), combo counter (capping at x4 dmg at x13 combo with venka prime. every other melee can only reach x3.75) and arcanes like fury (the best option imo)/ blade charger (meh option). you must use arcane trickery on your [Ash] aswell, as your 4 kills can proc it and trickery gives the same bonus to casting your 4 as smoke bomb does. another huge boost to his 4´s damage is subsuming [Banshee]´s silence and using its augment, [Savage Silence], as it increases the finisher dmg.

For a less specialized build, swap [Gladiator Rush] for psmite, [Quickening] for pfury, [Body Count] for glad might and [Drifting Contact] for organ shatterer. in this case you must have at least 1 dextery arcane on your gear to keep your combo up

The ash prime build for bladestorm: https://overframe.gg/build/188959/ash-prime/i-see-you-i-kill-you-ash/

mods that don´t increase the dmg ur 4 does: finisher dmg mods, cc mods, cd mods, status chance mods, base dmg mods (CO, PPP), elemental mods, range mods, [Berserker Fury] and smite mods

this build uses [Primed Reach] to make gaining combo easier, and CO to be able to deal some dmg to low lvl enemies, not to boost his 4 dmg. You can replace CO for [Gladiator Rush] to avoid killing enemies and build up the combo with ease