Overview
This is the oldest illustration in pixiv (the date of submission is 22:14 on 09/09/2007, but the actual date of writing seems to be within the year 2000).
The ID number of the contributor, 馬骨氏, is also "users/10," the youngest valid ID number (users/1 through 9 are treated as "resigned users," and we cannot confirm the details, but it is likely that the ID was created for testing purposes).