Apparently, Miki made both Sekai and Sakai frames. Sekai frames were manufactured by Miki and assembled by Sakai Export. It not uncommon for a manufacturer to produce more than one brand. The serial number format should be Myfxxxx, where y is a number designating the year and f is a letter designating the fortnight. The same serial number format shows on on some Norco and Centurion models, though it is unclear whether these frames were made by Miki or another manufacturer with the same serial number format. For instance, Merida of Taiwan uses the same format.