to preface this id like to say that I have had a lot of fun with this build only that it hasnt been tested in high SR. I wanted to make a build that uses a lot of skills from demo while still having the core nightblade in tact. The cold versions have better synergy with the ortus and nex set but its still quite allright as fire.
Neck: Vilgazors heart (you can also take ulzuins)
Rings: myth sapphire and ruby of elemental balance
Head: Justice set
Chest: Justice set
Shoulder: Justice set
Pants: Myth legwraps of tranquil mind
Belt: Cinderplate girlde
Feet: Myth wyrmscale footguards
Medal: Myth mark of divinity or korvaaks brand or anything firey
Weapons: Ortus and Nex or go with blazeheart and kirlians skullbreaker
playstyle: pneumatic always up and use firestrike to get to your target. You throw down a carpet of thermite mines cast mortar cast ABB, flashbang, BWC, blazing eruption, firestrike it to death.
Some pointers in building: I went for double seal of blades for pierce res armor increase and lifesteal. With the current setup its ~3 k da and ~3k oa with flashbang up. Components in the rings are optional as i simply ran out of mats to make something proper.
Upsides and downsides:
+many mechanics that save your life
+nightblade with firestrike
-requires quite some gear to even perform correctly