Reideen - Manga
Summary
From Cireus-Anime website: Saiga Junki is a normal high school boy who tends to be a little apathetic in general but who does manage to get better than average grades. When his archaeologist father, who went to investigate some ruins, is found dead, the family travels to the excavation site where Junki meets a mysterious stranger who gives him a ‘gift’: an ancient artifact that his father left for him …












In a system like that there would need to be rigorous documentation and certificates of prior ownership/guardianship or else anyone and everyone would just get grabbed off the street and enslaved at any time, and such a society would collapse instantly. So these slavers wouldn't have such documentation unless it was a forgery since the kids were just kidnapped; both offenses should be very serious capitol crimes. Once again, the day is saved by glorious Bureaucracy! (and the MC's knowledge and exploitation there of).