Can you explain the nine-year-old story behind the Sai portrait mentioned in the text?

The story of the Sai portrait is a fascinating one, detailed in Chapter 41. The narrator had a private discussion with a priest named Ismu, and they made a firm determination together that the portrait of Sai should be offered by the narrator. On the very day of this decision, the narrator presented the image to Sai. However, because Sai's meal was ready, the narrator had to leave quickly and couldn't explain the long story behind the portrait at that moment. The narrator intended to tell the story later, with the intention of doing so 'today or tomorrow,' but nine full years passed before an unexpected meeting occurred, which finally allowed the past history to be remembered and shared.