So I managed to do GR45 without losing any HP so this is good for Hardcore.
Just look at the Required items in the build and the rest is all optional but I think that what I used are the optimal choices.
You have to cast Desintegrate every 3 seconds for the whole rift to keep Taeguk buff up for massive dps and armor.
Your other 2 spenders (Meteor Shower and Explosive Blast) are cast by your Etched Sigil.
Main source of damage is Desintegrate but you might kite some bad affix elites so Meteor Shower will be your main dmg.
Meteor shower deals huge dmg with the Nilfur's Boast and your +%fire dmg so be sure to stack that a lot.
Explosive blast is used to keep a constant 4 stack on Orb of Infinite Depth for +20% dps and +60% dmg reduction.
Now for survivability, you only need the Halo of Arlyse and Ancient Parthan Defender combo for another huge dmg reduction bonus.
Also remember not to cast Meteor Shower directly to keep Aquila Cuirass up but you can sometimes cast Explosive Blast to make sure to always stay at 4 stacks in fights.
For more speed, try to group up mobs when your Convention of Elements is not on the Fire buff and then teleport in the middle of them to deal tons of dmg with Meteor Shower and the Audacity +30% dps within 15 yards.
Never forget to re-cast your Ice armor and Magic weapon buffs because the rift can last 10+ mins but with optimized gear and gems higher than 40 you can easily finish a GR45 within 10 minutes.
Using Templar with the resource regen skill will allow you to spam Desintegrate and Explosive Blast and stay above 90% arcane power.
Use the Invicible Token + The Ess of Johan for pulling. Rings dont really matter. Eun-jang-do is nice for RG freeze but really not required.
OTHER THOUGHTS :
You could also switch out Galvanizing Ward / Taeguk for Unwavering Will / Molten Wildebeest's Gizzard for similar results.
Hellfire Passive should be one of the 4 suggested passive or Unwavering Will for dps bonus. Blur could be used if you aren't used to the build or HC but is not required.