Blade of the House of Spiders

"So come. There in its depths… await all of me from every path, waiting with our blades drawn to cut down all of you."

The House of Spiders, a secret project between the 5 Fingers of the City, had the goal of creating a place where the Fingers can throw whatever they wish to be forgotten. You were chosen to be the Weapon due to your 'Unique' relationship with Time. Wielding the Arayashiki, a blade so sharp it cuts people out of existence itself, and the blade of the Dihui Star, you decided to cut your way out of the house instead, becoming Temporally Entangled in the process.

Temporal Entanglement - Level 3

"I will cut down every one of them. The Nursefathers, the House of Spiders, all that has been and all that will be."

Arayashiki and the Azure Blade
"Arayashiki leaves a blade wound that burns with implacable fire, this wound can never truly fade, as the wielder has slashed through the existence of their opponent at the cost of their Own..."
When you take this Subclass, you gain two unique longswords; Arayashiki and the Dihui Star's Azure Blade. Arayashiki is locked into its Scabbard until certain conditions are met.
You also gain proficiency with Improvised weapons.

Azure Blade;
Martial melee weapon. 1 Target. 1d8 (1d10) Slashing damage. Versatile.
When hitting a creature with this weapon, they are inflicted with 1 stack of 'Bladetrail'. For every 2 stacks of Bladetrail on a creature, you deal 1 additional slashing damage on a hit. Bladetrail expires at the end of combat Bladetrail has a maximum stack of 10. The Azure Blade counts as a magic weapon for the purpose of overcoming resistance and immunity to nonmagical attacks.
At level 7, this weapon becomes a +1 weapon, increasing to +2 at level 10, and +3 at level 15.

Arayashiki;
Improvised Melee Weapon (Sheathed)/ Martial Melee Weapon (Unsheathed). 1 Target. 1d6 Bludgeoning damage (Sheathed) / 8d8 Slashing damage (Unsheathed).
Arayashiki cannot be removed from its Sheath until certain conditions are met, which are stated in relevant subclass features.

Spacetime Afterimage Collapse
When you hit a creature with Bladetrail stacks, roll 1 additional damage die for every 5 stacks they have, as afterimages of you also strike the target. The additional damage dice from this feature do not benefit from any damage increasing effects outside of features specified in this subclass. This can trigger up to twice per creature per turn.

At the start of each of your turns, the DM chooses a hostile creature to gain 'Phantom Trace'. The first time you make an attack against a creature with Phantom Trace during your turn, regardless of whether the attack hits or misses, that creature takes 1d8 slashing damage and gains 2 Bladetrail. Phantom Trace expires at the end of your turn.
Creatures with Phantom Trace have an Afterimage of you poised to strike, positioned just out of their sight.

Blade of the House of Spiders
If there is an ally within 100 feet of you with any of the following subclasses, both you and that ally gain a +1 to attack rolls:
Index Proxy - [Oracle Device]
Middle Sibling - [Lævateinn]
Ring Maestro - [Corpus]
Thumb Sottocapo - [Precognition]

Multiple allies can benefit from this feature, but you only gain the benefit once.

String Severance - Level 7

"Maybe that irksome beeping will fall silent once I've cut you up into a shapeless thing and tossed what's left of you into some forsaken gutter."

Slay The Heavens - Tiansha
"The wielder has slashed through the existence of their opponent at the cost of their Own..."
When you reduce a creature to 0 hit points, you can choose to activate this feature. When you activate this feature, the creature instead remains a 1 hit point from that attack, and then you Unsheathe Arayashiki and make 1 attack against that creature before Sheathing it again. The attack with Arayashiki is guaranteed to hit. When reducing a creature to 0 hit points, it is Erased.
Features of the creature that activate on death, such as a vampire's 'Misty Escape' feature do not activate, the creature's body is destroyed in its entirety, and creatures forget about their existence. Creatures erased by Arayashiki cannot be restored outside of a 'Wish' spell or other similar effect. Creatures considered 'Outside' of time or otherwise immune to Time-based effects do not have their memory of the creature erased.
After using this feature, a random memory of yours is Erased, and you take (half your proficiency bonus)d6 psychic damage, rounded down. 
The DM chooses a meaningful but nonessential memory to erase.

After using this feature to erase a creature, you gain 1 'String Severance'. String Severance has a maximum stack of 4, and all stacks expire at the end of combat.
You gain bonuses depending on your String Severance stack:
1+ stacks; You gain a +1 bonus to attack rolls, and your movement speed increases by 10 feet.
2+ stacks; You gain temporary hit points equal to your fighter level at the start of each of your turns, replacing your current temporary hit points as normal.
3+ stacks; Whenever you take the attack action, make 1 additional attack.
4 stacks; When you miss an attack, the creature takes damage equal to 1 roll of your weapon's damage dice, excluding any damage modifiers.

For every 2 stacks of String Severance, 1 additional creature is inflicted with Phantom Trace at the start of your turn. If multiple creatures have Phantom Trace, they all get hit by the Phantom Trace attack.

Deathedge
When you hit a creature that has 10 Bladetrail stacks, you can expend all stacks on that creature to turn the hit into a critical hit. A critical hit from this feature deals additional damage equal to your Fighter level. Once you use this feature, you can’t use it again until the start of your next turn. You may still activate 'Slay the Heavens - Tiansha' if this feature reduces a creature to 0 hit points.

Lacerating Afterimages - Level 10

"Taxidermied and immobilized does the foe lie in the trace the blade has rent in space."


Rend Space - String Connection
When you have inflicted a total of 20 Bladetrail stacks in an encounter, or have reached 2 or more stacks of String Severance, at the end of your turn, this feature activates. This feature can only activate once per encounter.
When this feature activates, all creatures you choose within 50 feet of you take damage equal to two rolls of your Azure Blade's damage dice, and then you gain 'Shin - Dihui Star' until the end of combat.
While you have Shin - Dihui Star:
Your weapon attacks gain an extended crit range (19-20) if they do not have an extended crit range already.
Your movement speed increases by 10 feet.
You apply 1 more Bladetrail stack with attacks.

Formless Cut
Once per turn, if you have manifested Shin - Dihui Star during the current encounter, you can replace one of your attacks with a strike that echoes across time.
When you do, choose up to 4 creatures you can see within 40 feet of you. Each target must make a Constitution saving throw
(DC = 8 + your proficiency bonus + your Strength or Dexterity modifier). 
On a failure, The creature takes slashing damage equal to two rolls of your weapon’s damage die, and gains 2 Bladetrail stacks. On a success, The creature takes half as much damage and gains 1 Bladetrail stack.

Creatures with Phantom Trace have disadvantage on this saving throw.
You can use this feature a number of times equal to your proficiency bonus per long rest.

Echoshear - Level 15

"Breathlessly have I endured."
"Wretchedly have I yearned."
"Beyond all reckoning, I have cursed."
"And so, this moment, too, shall be Severed."

Rend Space - Echoshear
While you have Shin - Dihui Star, you may use an action to unleash a multitude of strikes, with the amount depending on your String Severance stacks. Once you use this feature, you cannot use it again until you Erase a creature with Slay The Heavens - Tiansha.
When you use this feature, you make 2 weapon attacks, targeting up to 3 creatures within 30 feet of you with each attack. You make one additional attack with this feature for each String Severance Stack you have. After making the final attack through this feature, all Bladetrail stacks on all targets are consumed, and all targeted creatures take slashing damage equal to the total amount of Bladetrail stacks consumed across all targets..
Each attack made through this feature only has the Attack roll rolled once, with the result being compared to all of the target's Armor class. Each attack made through this feature does not inflict Bladetrail. You cannot use Deathedge during Echoshear.

Muga, The State of Non-Self - Level 18

"The heavens themselves are not spared - heaven, earth, man, and the self. This star rises only for the one who perceives all existence and time as a single whole to sever them all."
"Wading Through a Dream, the Self Nowhere to be Found [無我夢中]"
"Like the Naraka of Avīci and Raurava [阿鼻叫喚]"
"Severed and Torn until Even the Form is Undone [支離滅裂]"

Erasing Me, Erasing You.
'I may lose control over my own mind, but I will make sure to run the picture through my head over and over.'
When you have 4 stacks of String Severance, and have used Rend Space - Echoshear at least once during the current encounter, you may choose to unsheathe Arayashiki and wield it properly, instead of using it as a glorified execution device.
While you have Arayashiki unsheathed through this feature, you may not use any other features of this subclass. While unsheathed, your movement speed increases by 30 feet, and you gain temporary hit points equal to twice your fighter level at the start of each of your turns.
Arayashiki deals 8d8 slashing damage while wielded through this feature and is treated as a martial melee weapon. Arayashiki ignores resistance and immunity to slashing damage.
Each time you make an attack roll with Arayashiki, you lose a random memory and you take 2d6 psychic damage. Whenever a creature enters a space within 10 feet of you, or starts its turn within 10 feet of you, it takes 2d8 slashing damage as afterimages of you slashing with Arayashiki dice them. A creature can take this damage only once per turn.
Whenever a creature is reduced to 0 hit points by damage you deal in this state, they are Erased.
While Arayashiki is unsheathed through this feature, it cannot be disarmed from you unless you willingly release it.
You may Sheathe Arayashiki at any time, ending this state, but once you do so you cannot unsheathe it again for 1d4 weeks.

The Effects of String Severance and Bladetrail are suspended while Arayashiki is Unsheathed this way.