FOTW describes a green flag with a white disc and a large red S, with no discernible serifs. The letter colour is unclear on the photographed container logo. A small website vessel photograph shows a white funnel with a dark top and a broad band presumed to be the flag; the source qualifies both the vessel identification and band interpretation.
Sanwa Marine carried on ship agency, cargo booking, brokerage, registration and towage, as well as container rental. Lloyds dates it to 1987; Mertens gives an apparent 1936 foundation and a Shinjuku, Tokyo base.
Keep the explicit scope label independent; no alias or company identity is inferred.