(Edit I am currently working on the page so please just know its not being raided and trolled)
Shikai can be unlocked at rank 10 while being a soul reaper.
Once rank 10 while in combat and under 10% health there is a 10% chance to unlock Shikai.
Types of Shikai include Zangetsu, Senbonzakura, Decay, Justice, Wind, Blood, String, Beast, and Ice