Chaos Blade

The Chaos Blade is a Katana in Dark Souls. It is forged from the Soul of Quelaag and can only be upgraded using Demon Titanite to +5.

Obtaining
The Chaos Blade is forged from the Soul of Quelaag and a Katana such as an Iaito or an Uchigatana that has been upgraded to +10.

Moveset
One handed R1: Brisk, vertical slashes. Good for bleed buildup.

One handed R2: Player brings the blade back over their offhand shoulder, and swings it forward forcefully. High starting lag. The move is so slow that attempting to use this on recovering enemies might give them time to actually get back up and retaliate, so only use for the killing blow.

Two handed R1: Brisk, vertical slashes.

Two handed R2: Player holds blade above his/her head, holds the end of the blade back with their left hand, and lets go, causing the blade to spring forward vertically. One of the slowest attacks in the game with little chance of hitting the opponent. If it does manage to connect, this attack will knock opponents off their feet. This move uses up a very large amount of stamina.

Kick (forward+R1): Standard kick.

Jump attack (forward+R2): Player jumps and buries the Chaos Blade into the ground. Tiny hitbox, but good damage.

Running attack: Running lunge. Good reach, but small hitbox.

Characteristics
The Chaos Blade drains 20 HP from the player with each successful hit, making it one of the only weapons that can kill its wielder. It does, however, deal good damage, and has some of the best dexterity-scaling in the game. Its moveset is very similar to the uchigatana moveset from Demons' Souls, so it may appeal to Demons' Souls veterans.

As with other Chaos weapons, the Chaos Blade scales with humanity. It also scales well with dexterity, although not as well as the Uchigatana or Iaito. However, the humanity scaling usually more than makes up for this.

The Chaos Blade has the potential for the highest damage of the eastern swords, with easily the highest physical damage with 10 humanity and 40 dex at around 450 damage per hit. Although it does not deal other types of damage and may do less nominal combined damage than, say, a Lightning Uchigatana, this is offset by the fact that the Chaos Blade does not have to bypass multiple defensive stats per hit. In practice, the Chaos Blade is the best eastern sword option for players who don't mind the feedback damage.

Like the other Katanas, the Chaos Blade causes bleed. The Chaos Blade causes more bleed than other Katanas.

Strategies
Against weaker enemies, using the Evil Eye Ring can help negate the damage caused by the Chaos Blade. Wearing Sanctus and/or using the Replenishment miracle will also help offset the feedback damage caused by the Chaos Blade.

Trivia

 * The Chaos Blade is similar to the Hiltless from Demons Souls', which also drained users' HP upon damaging its foe and had an uchigatana-like moveset.
 * The unique two-handed R2 attack for the Chaos Blade is identical to the two-handed R2 for the Uchigatana from Demons' Souls.
 * The Chaos Blade was going to be part of a side storyline involving Shiva of the East. This however was not present in the final game.
 * The Chaos Blade has the prefix "Chaos", but however does not deal fire damage like the weapon upgrade "Chaos".