For a time, Madarame was the only non-captain level Shinigami able to release his sword into Bankai form and Renji, whom he taught.
Madarame was the only non-captain level Shinigami able to release his sword into Bankai form. This was for a time. Madarame was the only non-captain level Shinigami able to release his sword into Renji. This was for a time. He taught Renji.