The legendary zanpakuto used by the substitute soul reaper Ichigo Kurosaki.
In its sealed state, the weapon is a Greatsword with 2d14+6 slashing damage. 
The item must be Attuned to your character in order for it to grow. Once Attuned, the power of the Zanpakto rises for how many minutes you've fought in combat during the time from when you first attuned. After fighting for a total of at least 30 minutes throughout the entire campaign, the sword will permanently turn into its Shikai state.

Shikai.

In Shikai form, any damage dealt while this weapon is equipped is doubled. Making its initial attack 4d14+6 slashing damage. The user may roll a 1d40 to allocate the amount of reiatsu points is gained at the start of a battle. All Reiatsu points are regained upon killing an enemy and 5 is regained off of each hit.

Flashstep.
Increases your movement speed to 1000ft.

Reiatsu Points.

The points can be used to do the following actions.
Flight (10 reiatsu points)
Lets you fly with a movement speed of 50000ft.

Getsuga Tensho(1 point).
 
As a bonus action, a blade of light rips across the ground. Doing a guaranteed 3 rolls of 12d30 +20  forcee damage.

Spiritual Pressure (2 points).

No action spended, opponents must pass a CON save (DC 14) or take 8d25 +10  bludgeoning damage that surpasses all immunities or resistances. Opponent has disadvantage on all of its attacks and takes 2d12 extra damage each turn for 1 minute. 

Hollow Mask (20 reiatsu points)

For 2 minutes, all damage done is tripled (Making Getsuga Tenshou do 36d30+20)

Bankai (40 reiatsu points)
The user must be able to say the words Bankai in order to use this move. Afterwards, your reiatsu explodes around you and all damage gets an additional quadruple modifier. If stacked with can  Hollow Mask it can make Getsuga Tenshou damage do 144d30+20. Every Reiatsu point abillity has its cost ignored and now instead the user generates Shinigami points (1 for killing an enemy or in Dangai form, for each attack)

Soul Society Support (1 Shinigami Point)

Call a member from the Soul Society 13 Courts Guard Squads to assist you depending on a 1d5 roll, and afterwards roll a 1d2 to choose between each attack

1: Rukia Kuchiki: 1: Hakuren: Rukia shoots out a beam of ice doing 2 rolls of 80d30+40 Long Range of 8000 ft Ice Damage. Hits enemys behind the target.
            2: Tsukishiro: Rukia dashes forward 500 ft and attacks with an AOE attack that stretches 800ft.. Making a giant ice circle, It can catch any flying enemy and has an infinite vertical range. Does 2 100d20+20 damage.
2 Renji Abarai: 1: Hikotsu Taiho: Single Target Shoots out a condensed ball of energy that has does 10000ft. 100d50 + 30 force damage that knocks back the opponent 50 ft on hit.

2: Zaga Teppou: Renji uses his true Bankai form and stabs one opponent in a range of 5 feet , they must pass a CON SAVE (DC 14) or have their HP halved 

3.Kenpachi Zaraki: 
1.Are you strong?: Choose between any creature or object, on the field including yourself. Kenpachi will teleport to them regardless of distance and enter a stance. If an opponent tries to attack the creature or thing, he will negate it and must pass a DEX save (DC 15) to take half of 200d60+30 damage. 
2. Trade off: Kenpachi releases his Bankai and does 200 damage to the user out of rage, afterwards he rolls a 1d20, if it doesn't crit halve the HP, if it does instantly kill one opponent. The user can choose whether to use this ability or not. If not, reroll the initial choosing of the 13 courts guard member.

4. Byakuya Kuchiki:
1. Scatter: Byakuya uses his Shikai Ability which allows him to roll a 1d20 + 11, boosts AC for 2 turns depending on the roll.

2. Shūkei: Hakuteiken: Byakuya does a guaranteed 40d20+30 damage. Boosts AC by 10 afterwards and lets you engage flight if not already in flight.

5. Ikkaku Madarame:
1. Ryūmon Hōzukimaru: Increases Attack power by x5 for 5 turns
2. Tough Customer: For 5 turns and Halves all damage taken. If a resistance to the damage is in effect, make it an immunity.

Dangai Form. 
Permanently sacrifice all of your special abilities to change your basic attack action to an infinite range attack that halves HP on every hit and boost your AC by 20 permanently (As long as this weapon is equipped.

Final Getsuga Tenshou (30 Shinigami Points)
Can be done from Bankai form and Dangai form. Sacrifice your weapon to instantly kill all enemies on the field no matter who it is and what they are. Ignores all damage immunties and resistances. 

Proficiency with a Greatsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Can be Attuned by any melee class, Heavy, Two-Handed, Graze