What is the story behind the placement of the Sai portrait mentioned in the text?

The story involves a mutual decision between the narrator and a priest named Ismu. As recounted in Chapter 41, they made a firm determination that a specific 'portrait of the powerful Sai should be kept right here' and that the narrator himself should be the one to offer it. After presenting the image, the narrator had to leave quickly because the recipient's meal was ready, preventing him from sharing the long story behind the portrait. He intended to tell it later, but a full nine years passed before an unexpected meeting allowed the history to finally be shared.