I had a favourite shirt-pocket size cassette player in 1982-3 and it was a red Aiwa with a manual radio built in to the lid. The smart thing about this model was this -- if there was no cassette in the machine then you could close the lid down, making it smaller and cuter. It took a single AA, too, but it was forever going wrong so I exchanged it. Who knows the model number please??
Are you sure it was an AIWA? I know no AIWA that makes smaller without cassette, but I indeed know some SONY, like the WM-10 or the WM-F10 with radio.