OOZ662 over 9 years ago There's a "Mini" logo on it. Thinking MiniCDs and the one in her mouth is in a case.Personally, I dunno if they were ever made as "cartridges" like the PSP's UMDs, but if they were, that might be it.
user 201502 almost 9 years ago According to artist's commentary on pixiv it's a Sony MZ-N910, which is a portable NetMD recorder.