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Hello and welcome to this Grail of Infinitude - Support Comparison!
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I hope I'll be able to help you, let's start!
✦ Table of contents ✦
Short Introduction
Team Selection
Support Buff Comparison
DMG Comparison
Conclusion
✦ Short Introduction ✦
The Astral Ring Specialization [Grail of Infinitude] (GoI) was introduced in 8.3 with Planar Armament: Warped Spacetime.
It focuses on Ultimate spam and SP consumption, sharing the SP among the entire team. For more details you can read this Guide:
Currently five battlesuits can support this specialization:
PA - Planar Armament: Warped Spacetime - Helia
PS - Peregrine Sword - Li Sushang
HoHE - Herrscher of Human: Ego - Elysia
RS - Reign Solaris - Durandal
FWS - Ba-Dum! Fiery Wishing Star - Kiana
Helia can't act as support yet as she's the only GoI dps available. Four support options left that leaves 6 possible teams, so let's compare them~
✦ Team Selection ✦
First let us take a quick look at Helia's team requirements~
✧ Planar Armament: Warped Spacetime ✧
Lightning - BIO
Notes on her team selection:
✧ Pretty much all of her bosses are PSY-type, no typeless/BIO bosses covered
✧ Elemental DMG cannot crit.
✧ Deals melee DMG
Really not much to say 
✧ General Hints ✧
Summary: Buffs spread on many different scaling is better than to focus on one scaling, Vulnerability and especially Breach buffs are more valuable buffs due to how rare they are.
Full version:
In Honkai Impact different scalings are calculated independently of each other, which is why you want to not focus your buffs on one stat but spread them over many different ones.
As example: Your Ba-Dum's Basic ATK deals 1000 DMG
(Option 1) you give her 100% Fire DMG
➔ 1000 * (100% + 100%) = 1000 * 2 = 2000 DMG
(Option 2) you give her 50% Fire DMG and 50% Total DMG
➔ 1000 * (100% + 50%) * (100% + 50%) = 1000 * 1,5 * 1,5 = 2250 DMG
So the more different scalings the better~
Additionally most characters have mostly Elemental/Physical DMG and Total DMG as their self buffs.
For example Ba-Dum has following self buffs in her kit and gears (only counting buffs that affect all attacks):
✧ 243% Fire/Elemental DMG
✧ 123% Total DMG
✧ 62% Fire/Elemental DMG taken
✧ 40% Total DMG taken
As you can see vulnerability buffs are way more than basic Elemental DMG or Total DMG and that counts for all characters, making Supports who give a lot of vulnerability worth more than Supports who give a lot of Elemental/Total DMG.
Additionally self Breach is extremely rare, making Breach in Supports very valuable. Ba-Dum's only self Breach is 6% for her Basic ATK.
Impair or Elemental/Physical Breaker states do not stack and you can have one buff of each at max (self-Breach excluded). As every P2 Physical DMG dealer so far has Impair, Impair doesn't have any value in Supports currently.
For highest efficiency you want to add two supports that either balance out each other's weaknesses or two Valkyries who don't show huge weaknesses in their buffs.
✦ Support Buff Comparison ✦
✧ Planar Armament: Warped Spacetime ✧
Notes:
✧ Helia can inflict Paralyze Trauma
✧ I cannot test her SO rotation as Support yet
✧ Overall her rotations are rather long
✧ Peregrine Sword ✧
Notes:
✧ Sushang has really good hit count
✧ Sushang has Bleed Trauma
✧ rather slow rotations
✧ Ba-Dum! Fiery Wishing Star ✧
Notes:
✧ Kiana has an advantage in case a fire GoI DPS ever releases
✧ Really fast rotations
✧ Great buffs spread among the multipliers
✧ Herrscher of Human: Ego ✧
Notes:
✧ While her buffs look bad on paper she's actually pretty fine in battle, idk
✧ Reign Solaris ✧
Notes:
✧ Her buffs are really meh overall, not great
✧ Only GoI Support that provides Shield Break
✧ Fast rotations considering QTE only works to activate all buffs
✦ DMG Comparison ✦
Notes: These numbers are not always accurate and can differ based on the stage you're fighting. All tests were on a typeless enemy and include one AR Charing and one Stellar Outburst rotation.
All characters are S0 with a Sync 1 weapon
I'll make it prettier later if I have the time
All rotations are around the same in the end because of how much time Helia actually consumes
✦ Conclusion ✦
All the Supports are pretty usable so far, so use whatever you have~
For most cases Sushang/Kiana will be best for Helia.
For Symphony Kiana/Elysia should be best, Durandal is pretty much limited to Shield Break so far~
Elysia and Kiana might come out even better if a future GoI Valkyrie is Ice / Fire. Other than that we might get a Breach provider for this specialization in future, so stay tuned 
- Love to Inari
- Website for official wallpapers in case you're interested, here
Thank you for reading my guide, I hope I was able to help you!
Have a great day and fun with your Grail of Infinitude Valkyries~ 
