Guide
How the kit works
Start with Quadrivalent Ascendance when you can. It immediately defeats normal enemies without entering combat. At the start of each wave, it deals Lightning DMG equal to 200% of Acheron's ATK to all enemies and reduces Toughness regardless of Weakness Types. After her Ultimate, Quadrivalent Ascendance also gives her 1 Slashed Dream and places 1 Crimson Knot on a random enemy.
Red Oni gives Acheron 5 Slashed Dream at the start of battle and places 5 Crimson Knots on a random enemy. Use Octobolt Flash to gain another point and place a Knot on your chosen target. It also damages adjacent enemies. Trilateral Wiltcross is a single-target attack when you need to use it instead.
Atop Rainleaf Hangs Oneness adds 1 Slashed Dream and 1 Crimson Knot when a unit inflicts debuffs with an ability. It triggers only once per ability use, even if that ability debuffs several enemies. Knots move to another enemy when their target leaves the field or is defeated.
At 9 Slashed Dream, use Slashed Dream Cries in Red. Choose targets for three Rainblade hits; each removes up to 3 Knots and deals extra damage to all enemies when it removes any. Stygian Resurge then hits all enemies and removes the remaining Knots. Thunder Core increases Acheron's damage when Rainblade hits targets with Knots and adds six random hits to Stygian Resurge.
Build and why
For relics, use four pieces of Pioneer Diver of Dead Waters. Its two-piece bonus increases damage to debuffed enemies by 12%. The four-piece bonus gives CRIT Rate and increases CRIT DMG against enemies with at least two debuffs; those effects double for one turn after the wearer inflicts a debuff. Scholar Lost in Erudition is an alternative that boosts Skill and Ultimate damage.
For planar ornaments, use Izumo Gensei and Takama Divine Realm. It gives 12% ATK and another 12% CRIT Rate when a teammate follows the same Path as Acheron. Inert Salsotto is an alternative: at 50% CRIT Rate, it increases Ultimate damage by 15%.
Along the Passing Shore is the first Light Cone choice. It gives CRIT DMG and applies Mirage Fizzle when Acheron hits an enemy, increasing her damage against that target. Incessant Rain is another option, with CRIT Rate against enemies carrying at least three debuffs. Holiday Thermae Escapade is a four-star option that can inflict Vulnerability after an attack; Good Night and Sleep Well increases damage for each debuff on the target, up to three.
Choose CRIT Rate or CRIT DMG on the body, ATK Percentage or SPD on the feet, and Lightning DMG Boost or ATK Percentage on the sphere. Use ATK Percentage on the rope. For substats, prioritize CRIT Rate, then CRIT DMG, ATK Percentage and SPD.
Leveling priority
Follow the game's order: level Slashed Dream Cries in Red first, then Octobolt Flash, Atop Rainleaf Hangs Oneness and Trilateral Wiltcross. The Ultimate is her main source of damage, while the Skill is an attack you use to build Slashed Dream.
For maximum ascension, you need 308,000 Credit, 65 Shape Shifter's Lightning Staff and 15 each of Dream Collection Component, Dream Flow Valve and Dream Making Engine.
For all skills, the total is 3,000,000 Credit, 8 Tracks of Destiny, 18 Fiery Spirit, 69 Starfire Essence, 139 Heaven Incinerator and 12 Past Evils of the Borehole Planet Disaster. You also need 41 Dream Collection Component, 56 Dream Flow Valve and 58 Dream Making Engine.
Eidolons worth it
Mute Thunder in Still Tempest is worth considering for team flexibility. It reduces the number of other Nihility characters needed for the highest The Abyss bonus from two to one. It also gives Acheron 1 Slashed Dream and places 1 Crimson Knot when her turn starts.
Apocalypse, the Emancipator is another large upgrade to consider: it gives the Ultimate 20% All-Type RES PEN, and makes Basic and Skill damage count as Ultimate damage. Silenced Sky Spake Sooth is useful for its 18% CRIT Rate against debuffed enemies.
If you are stopping short of E6, E3 and E5 are lower-priority stopping points to consider skipping: they raise skill levels rather than adding the team flexibility of E2. E4 gives enemies 8% Ultimate DMG Vulnerability when they enter combat.
Teams
Without E2, a good starting point is two other Nihility characters and a sustain. The Abyss raises Acheron's Basic, Skill and Ultimate damage to 160% of their original damage with two other Nihility teammates. Their ability to inflict debuffs also helps her Talent build Slashed Dream.
Cipher, Jiaoqiu, Silver Wolf and Pela are listed options for the Nihility slots. Mortenax Blade is another Nihility option with debuffer and sustain tags. For a separate sustain, Dan Heng • Permansor Terrae or Huohuo are options named by the guides.
At E2, one other Nihility teammate is enough for the highest The Abyss bonus, leaving more room for a buffer such as Tribbie or Sparkle. Teammates do not need to share Acheron's Lightning type; the important considerations are their Path and whether they can contribute debuffs or support.
Common mistakes
Do not expect several debuffs from one ability to give several Slashed Dream points through Atop Rainleaf Hangs Oneness. Its effect triggers once per ability use. At the 9-point limit, extra points instead give stacks of Quadrivalent Ascendance, up to three.
Do not ignore Crimson Knot placement during Slashed Dream Cries in Red. Rainblade removes up to three stacks per hit, so aim at targets with Knots to trigger its extra damage and Thunder Core. Crimson Knot cannot be applied during the Ultimate.
Do not choose Inert Salsotto and forget its 50% CRIT Rate requirement for the Ultimate damage bonus. With Izumo Gensei and Takama Divine Realm, remember that its CRIT Rate bonus requires a teammate on the same Path.
