Originally Posted by
Hummer
...Some of the serial numbers from Hong Kong and Korea were just a number, which the serial number on your Sekai appears to be.
The best I can conclude is that the Sekai is for the 1984 model year, but no idea who made the frame....
Given that it is a purely numeric format from the mid 1980s, I'd be checking the rear dropouts too, just in case it is a Giant manufactured frame. We've haven't seen any Giant manufactured Sekai yet but the Giant manufactured Nishiki from this era had a purely numeric serial number on the BB shell and a Gyymm format date code, typically on the non-drive side rear dropout.