Time to slash!

   Hi.  Please be aware that spoilers are swarming in this thread. If you've only just started reading/watching Bleach, I strongly advise you to avoid going further.
I won't state basic info, since it could be about stuff you might not know yet. I'd hate to ruin the fun of discovering it.
   
   To those who're already swimming, mind your safety jacket. What I'll hide in spoilers is everything revealed in the Last Arc (Thousand-Year-Blood-War). Adding updates means that if you're not following the rythm of weekly chapters, you also might end up learning stuff you'll regret.
   In any case, never think twice before asking me for info. Tell me which Chapter you're at, I'll check and tell you what you need without spoiling the rest.

   Enough bold typing already.You've been warned, here comes:

Generalities about creating your own Zanpakutô:

• A Zanpakutô -Zan for short- may take various aspects of Japanese feodal blades, from a short tantô knife to long nodachis. When creating your character, remember that you can easily wield something different from the katana. You can use the following list to create your sealed form and/or released form (click the name to see the pics): 
  

  Swords:

  Spears, axes, maces:

   
  

  Short blades:

   
  

  Other exotic stuff:

  
  

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• Note that as its wielder gets stronger, he/she has to mentally communicate with the Zan in order to manifest its power. Meditation being the best way to get to this point. Never hesitate to add talks with your Zan, especially during fights, marked within the symbols { ... }
  

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• Don't forget that there is a very strong relationship between the Zan and its owner. Being more than a mere blade, a Zan also evolves as the owner gets stronger. A Shinigami and its Zanpakutô always share very similar personalities. If you're hot-headed, your sword soul will also be eager to fight. On the opposite, if you're calm and mesured, your Zan will act the same way. Use that when you char is communicating with your Soul Cutter.
  

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• The specific power inside the sword can be released. Get a release command that matches the power of your Zan best.
  

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• A Zan is unique. Hence, each power is unique. Be original and you'll be praised and have fun. Copy-paste stuff and I'll personally spank your butt. 
  

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• When a Zan is released, its shape changes, becoming what's called "true form". Find something smexy.
  

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• Acquiring Bankai is allowed. However, it must be properly justified. Kageshi Tsurai is a Captain, so it's legit. Mine is nowhere near mature even in spite of years of harsh training. Etc.
  

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• Don't hesitate to add pics or drawings in your intro to let us better understand what it is you're wielding.
  

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Your Senpai, Hiro.

Here goes  List of Shikai / Bankai (by character, in alphabetical order):

Note- I'll use alphabetical order with the name that's most referred to.
The Japanese place the family name in first position (which is what I did for my char) and use it to name people in a polite way.
Once they're getting close friends, they use the "first name". 
Example: Abarai Renji is better known as Renji (his first name). You'll find him at "R".
Kuchiki Byakuya will be found at "B", even though his family name is the same as his sister's Rukia, who you'll find at "R".
On the other hand, characters such as Komamura Sajin or Aizen Sosuke will be found through their family name, since it's the one you know them by the best.


Aizen Sosuke:
   Shikai: "Shatter, Kyoka Suigetsu (Mirror Flower, Water Moon)".
Special ability Kanzen Saimin (Complete Hypnosis) allows him to fool his opponents (in an insanely powerful way). Anyone who's seen Aizen's sword release even decades ago gets under its spell. It then allows Aizen to create illusions and deceive the 5 senses every time he activates his Zan's power.
Note: After the Arrancar war, Aizen has definitely lost his Zanpakutô. Because godlike.

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Kuchiki Byakuya:
   Shikai: "Scatter, Senbonzakura (Thousand Cherry Blossoms)".
The blade is split into thousands of flying fragments. They can be controlled with the remaining guard, and used to both mince enemies from afar and as a protective shield. A safe zone around Byakuya lets him breathe even while the blade petals swing close around him. 
   Bankai: Zenbonzakura Kageyoshi (Vibrant Display of a Thousand Cherry Blossoms).
Dropping his katana to the ground (letting it dissapear into it as if the ground were water), Ichigo's uncle can manifest a massive version of his Shikai.
Although mentally controlled, directing the blade petals with his hands increases their speed greatly.
Patterns: 
              Senkei (Slaughterscape): The blades are condensed into a thousand swords that circle around in rows, trapping Byak' and his opponents. Focusing on offense, this pattern allows him to wield any sword from the rows with the attack power of all of them. A slash from one of those condensed blades deals much heavier damage than multiple slashes from the petals. While wielded, each sword can be scattered in petals again.

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Hitsugaya Toshiro:
    Shikai: "Reign upon the frozen heavens, Hyourinmaru (Ice Ring)". The katana blade grows longer, and a chain appears at the end of the hilt, terminated by a crescent-shaped blade. 

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Madarame Ikkaku:
   Shikai: "Grow, Hozukimaru (Demon Light)". Ikkaku's katana fuses along with his sheath (both used while fighting), turning into a spear (yari). This form obviously increases the reach of the weapon, as well as its defensive power.

Picture:

Special ability "Split" further transforms the Zan into a three sectional staff (sansetzukon). The parts, connected by chains, allow Ikkaku to deal mid-range attacks in a very versatile way.

Picture:

   Bankai: "Ryumon Hozukimaru (Dragon Crest Demon Light)". Once the three parts are slammed back together, they turn into three different weapons, still connected by chains. One end is a monk spade, the other is a guandao (crest-like heavy blade), and in the center lies an axe blade. All three are absolutely massive and can float in the air. Ikkaku's bankai doesn't come with special abilities, but rather functions on par with its wielder. The longer the fight drags on, the more powerful it becomes, as the dragon engraved in the center blade turns crimson. It's just about plain badass brute destructive slashing!

Picture:

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Let's keep it up!
I'll continue from a new post cause editing stuff with all the pics in spoilers started to get messy.

Kotetsu Isane:
    Shikai: "Run, Itegumo" (Frozen Snow).
It has only been shown once, years ago, and extremely briefly. I'd love to know more about it, but I guess this is a wait and see option. The only thing we know is that her katana transforms into a 3 branch sword as follows:

Picture:

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Kira Izuru:
    Shikai: "Raise your head, Wabisuke" (The Penitent).
The blade "rotates" to end up forming 3 sides of a square (refer to pic below).
Each time the blade hits an object, it doubles its weight. Such effect is exponential and Kira uses it to literally take down ennemies.
Last but not least, he may then behead them with the square side of his sword.

Picture:

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Kenpachi Zaraki:
    Shikai: the Captain doesn't communicate much with his Zan, if at all. However, the worn-out nodachi has greatly increased cutting power, as Kenpachi keeps boasting that he can cut through anything. Which, in most cases, appears to be true.

SPOILER FROM THE FINAL ARC. YOU'VE BEEN WARNED! THE REST IS UP TO YOU!: