"On the Way to a Smile" is a set of two stories by Kazushige Nojima (AC's scenario writer) featured in the back of the book Final Fantasy VII: Advent Children - Prologue; the first story can also be found on Square Enix's Japanese-language Advent Children site. These two tales are titled "Case of Denzel" and "Case of Tifa", and are intended to both embellish and fill some gaps in AC and FFVII's stories.
In February 2007, official English translations for these two stories became available via the Region 1-released AC Collector's Edition. Additionally, a third story, this time about Barret, made its debut in this set.
Here are the three stories. "Case of Denzel" and "Case of Tifa" were translated from the Japanese by Xcomp and revised (for clarity) by Reeve. Xcomp's raw translations, as well as some other AC-related information, can be found at their site, FFVII Web Novels.
Special thanks goes out to Digital Holocaust, who first posted information about this story in the Forums, and Sephiroth OWA, who has also kept the Citadel updated.