When does inuyasha's sword achieve crystal mode?

Inuyasha's sWord the Tessaiga achieves Crystal Mode in the episode titled "The Fate of the Tessaiga" from Inuyasha Season 3. During this episode Inuyasha battles the powerful monster known as Ryukotsusei and is unable to defeat it. After receiving advice from Totosai he is able to unlock the sWord's true potential and transforms it into Crystal Mode. The sWord initially starts out as the normal red-colored steel form and when it transforms to Crystal Mode it turns into a blue crystalline state.

In order to transform the sWord into Crystal Mode Inuyasha must perform several steps:

• Gather the shards of the Shikon Jewel
• Combine the shards with the Tessaiga
• Perform the "Backlash Wave" attack

After performing these steps the sWord will then transform into Crystal Mode allowing Inuyasha to use its full power and defeat Ryukotsusei.