True Vide the Wicked Guide (100% consistent, no nuts) - Octopath Traveler II

Here's a foolproof way to beat Octopath Traveler 2's hardest boss. Compared to my prior no-nuts kill, this one can be done at lower level, doesn't need to reveal weaknesses on a prior attempt, requires less precise speed stats, and uses virtually zero limited supply items (just 2 reinforcing jams, of which there's 18 in the game). Throne and Hikari are level 70, and the rest don't need levels (I had them at level 40).

Gear and Support Skills:
note: if a slot is left empty, you can add whatever, unless stated otherwise.

Throne (Armsmaster) - Deal More Damage, Summon Strength, Lasting Memory, SP Saver
Weapons: Battle-Tested Blade, Lionheart's Axe, Giant's Club
Equipment: Bodyguard's Vantage, Art of Disguise, Butler's Tailcoat, Alpione's Amulet, Finisher's Claws
notes: needs to be level 70 or higher (though fortifying nuts can compensate for levels)

Hikari (Cleric) - Deal More Damage, Peak Performance, Elemental Augmentation, Of Equal Might
Weapons: Firestarter, Thunder's Roar, Bellowing Baton (or Thunder Mace)
Equipment: Giant Shield, Mermaid Circlet, Blessed Vestments, Elemental Augmentor (or Laila's Amulet), Fang of Ferocity
Other: Chimera as a learned skill, plus you need to have 2 weapons in your inventory with 375+ physical attack (don't worry you won't lose them). I used gravity lances, which can be bought from the roque island armourer, but literally anything will do.
Notes: Needs to be level 70 or higher, and needs to be slower than Throne.

Partitio (Dancer) - Hale and Hearty, Upgraded Accessories, Hang Tough, Purification
Weapons: any dagger or spear that boosts accuracy, if necessary (tonfa is good)
Equipment: Can use whatever, as long as he has 410+ in both defence stats, 5700+ HP, and 225+ accuracy with either his dagger or spear. I used Platinum Shield, Platinum Helm, Royal Guard's Mail, and 2 Empowering Bracelets.
Other: has the 10 Strength Cleric from Canalbrine (Divine Protection) as a follower
Notes: must be slower than Throne. Giant Shield and/or Cursed Armour can help with this.

Agnea (Inventor) - The Show Goes On, Hale and Hearty, Hang Tough, Purification
Weapons: Double Tomahawk
Equipment: Can use whatever, as long as she has 410+ in both defence stats, 3700+ HP, 275+ speed (to avoid crits), and 225+ accuracy. I used Protector's Shield, Dazzling Tiara, Royal Guard's Mail, Mikka's Amulet, and Empowering Bracelet.

Castti (Merchant) - A Step Ahead, Boost-Start, Hale and Hearty, Purification
Weapons: any speed-boosting axe, if necessary (stupefying stone axe is good)
Equipment: Thunderstorm Amulet, plus whatever equipment you want, as long as she has 450+ physical defence, 5300+ HP, and 275+ speed (to avoid crits). I used Platinum Shield, Dazzling Tiara, Royal Guard's Mail, and Empowering Necklace.

Ochette (no subjob, but can use apothecary for added bulk) - A Step Ahead, Boost-Start, SP Saver, Purification
Weapons: None
Equipment: Thunderstorm Amulet, plus whatever equipment you want, as long as she has 96+ SP, 450+ elemental defence, and 2200+ HP. Could alternatively aim for 96+ SP, 350+ elemental defence and 2700+ HP, whatever is easier.
Other: Ettin Snake, Headless Horseman, any mid to high level beast that hits twice with spear/dagger/axe/ice/lightning/light (I used a Vagrant Frogking II), and any (non-boss) beast with an AoE ice, wind, or dark attack (I used Dreadwing).
Notes: this build is slightly different from what I used in the video, as it turns out my build was way overkill on the defences and didn't have enough SP (hence the addition of SP saver).

Temenos (Conjurer) - The Show Goes On, A Step Ahead, Boost-Start, Purification
Equipment: 2 Lightning Amulets, speed boosting equipment as necessary

Osvald (Merchant) - A Step Ahead, Purification
Equipment: None. However, if you don't give him anything there's a very small chance that you can lose on turn 9. Giving him 2 lightning amulets fully prevents losing, but any defensive gear can help instead.
Notes: needs to be slower than Temenos (can use speed reducing gear to achieve this).
If you're too lazy/broke to grab the second merchant license, as long as you have an ancient cursed talisman you can skip giving Osvald a subjob at all.

Note: Try not to exceed the HP requirement on Castti by too much. If one of the bottom party's characters is absurdly tanky due to nuts (unlikely), give them the shield of strength.