To find how to get them, please ask someone ingame. Lazy me~. It may not be accurate due to me not knowing this game, but it'll give u an idea. This is the part I typed in sore's guide. All others is his, but this part is mine. Ask him if u dont believe it. Im tired of explaining.

Zanpaktou Abilities
Ichigo: Die once for shikai, master bankai with attacking thin air.
Shikai- Cannot be turned off or named.
Getsuga Tenshou- A 3 tiled wave of reiatsu.
Bankai- U get a cool robe. You also have faster attack speed... but lower dmg. U can rack up more dmg then in shikai with attack in ten secs anyway so it wont matter.
*(Kuroi)Getsuga Tenshou- 5 tiles wide. Fairly strong and accurate.
*-The word Kuroi is not there. It is in my bleach source. mmm

Hitsugaya(Shiro chan! ^^): Shoot ice dragons. For bankai, hit ppl.
Shikai- You learn ice dragon. It shoots a quite good projectile that can freeze. It might not phase them at times tho so bware.
Bankai- Love da chicken wings =D. U still got ice dragon. But now, when attacking u may shoot a short ice dragon for 3 tiles.

Ikkaku: Master both shikai and bankai by attacking.
Shikai- Extends about 3 tiles I think when u attack.
Bankai-TRIPLES ur str. U might be slower. With a good str like that, just chop away to massacre them.

Kenpachi: Master both by killing...
Shikai-boosts ur str and def I think
Bankai- More boost

Gin: Master by attacking. Has no bankai
Shikai- Master it... and... Long sword... too long.. no bankai I believe.

Hinamori: Attack the wall with ur shikai... nuff said
Shikai- A better byakurai. I lack info on this one. O yea, u shoot rei balls on each attack.

Renji: Master both by attacking.
Shikai- Same as ikkakus, 3 tile extend.
Bankai- Summons a thing u move with ur arrow keys and makes u move with the mouse.... uh huh... btw, no matter what, the dmg for this always is the same, so... if u can hit them with this, their dead XP unless they got good hp of course

Byakuya: Master by moving pedals onto ppl to hurt them.
Shikai-Summons few rei based pedals.
Bankai- Summons a lot of rei based pedals. You can also use senkei to melee them. Also, thru a bug I wont tell, u can get lots more pedals.

Jiroubou: Master same way as byakuyas.
Shikai- Str based blades thing.
Mastered shikai/bankai- More blades... no new things. Theres bugs which let u fill the screen with them but not saying. If u have too much, relog.

Kira: Master by attacking?
Shikai: Supposed to lag opponent, and it hits everyone if they are next to u. Even behind u. So some say. No bankai.

Yumichika: Master by attacking.
Shikai- Useless until mastered. When its Mastered Shikai, u learn cyclone dance. This takes their hp from them and gives some to u.

Mayuri: Master by attacking.
Shikai- Useless.
Bankai- A poison fog of 3 tile straight line upon attacking. Can block incoming cero and other projectiles. U also get a caterpillar on u.

Rukia: Master by attacking with tsukishire.
Shikai- Just attack as tsukishire is random while hitting ppl. When mastered, u get hakuren in bankai, which looks like a altered hitsugaya dragon. Master bankai by hakuren and tsuki.