The Developer of the Modified Souls

 is the three hundred and thirty-seventh episode of the Bleach anime.

As Yoruichi and the captains battle the Reigai, Ichigo, Kon, and Kisuke go in search of Inaba's lab.

Summary
Yoruichi explains that she had sent word to Kūkaku Shiba about the situation and she arrived with Jidanbō Ikkanzaka and Ganju Shiba to assist the captains in their fight with Inaba. They then healed their injuries at Kūkaku's home and waited for an opportunity to strike back. Kenpachi attacks the Reigai and tells Ichigo, Urahara and Kon to get out of the way. Yoruichi tells the trio to leave the Reigai to them and they leave as the captains begin the fight.

Ichigo sluggishly follows Urahara and Kon until he collapses, his eyes having begun to turn black. He awakens in a warehouse where he is told by Kon that he nearly turned into a Hollow again. Urahara explains that the balance between his Hollow and Shinigami powers is breaking down and reluctantly asks him to remain there. Kon tries to be supportive, saying that he will restore Ichigo's Shinigami powers. After Ichigo remembers Kon's words before they left the Human World, he tells Kon that he is counting on him and hands him the Reishi collector. Urahara binds Ichigo with Kidō and they leave him. When Kon asks if it was necessary, Urahara states that it is to be safe, but that he is uncertain if it will help.

At the S.R.D.I., as the captains battle the Reigai, Kon angrily asks Urahara why they are at the back door of the S.R.D.I. when they had just fled from there. Urahara explains that he was trying to throw the enemy off their trail and states that he wants to investigate the 12th Division, Inaba's unit. He mentions that there is little left from his time as captain of the Division, which surprises Kon, who thinks this means that he knew about Inaba. Urahara tells him that Inaba had not joined the Division when he was still in the Gotei 13. He succeeds in gaining access to the computer records and learns that Inaba joined the Gotei 13 sixty years ago. They then go to a library where Urahara checks the records of each Division's recruits and discharges between his exile and Inaba's first appearance. They then head to the 10th Division, with Kon complaining about Urahara's secretiveness.

Kon and Urahara evade Shinigami patrols. Urahara reminds Kon about Nozomi's and Inaba's differing accounts of their origins. He explains that they were both a single Mod Soul based on the developer of the Mod Souls. He states that he had been searching for evidence of a Shinigami who disappeared prior to Inaba's arrival, but the 12th Division records had been erased and in the library, he found evidence of the information in the 10th Division's records from ninety-six years ago being altered. Urahara finds the record of Yushima and concludes from the record that he is in the Nest of Maggots.

There, they are confronted with two Reigai. After defeating the Reigai, Urahara and Kon finds Yushima slumped in a chair in a cell. As Kon tries to wake him, Urahara notes that he may never regain consciousness. Meanwhile, Ichigo escapes from his restraints, fully Hollowfied.

Shinigami Illustrated Picture Book
Tōshirō thinks of how everyone managed to heal quickly while at Kūkaku's house and is thankful for it. He then recalls how every night he saw Byakuya going off somewhere. He also then recalls the sound of wood being chopped soon after. Tōshirō starts to believe that Byakuya was training, only for the screen to pan and show a large wooden Wakame Ambassador statue behind Kūkaku's house.

Fights

 * Gotei 13 vs. The Reigai

Powers and Techniques Used
Kidō used:
 * Unnamed Kidō (flashback)
 * Bakudō #99 Kin (禁, Seal)

Techniques used:

Zanpakutō released:

Shikai:
 * (flashback)
 * (flashback)
 * (flashback)
 * (flashback)
 * (flashback)

Bankai:
 * (flashback)