Was the box shaped like a squid?
https://ameblo.jp/ekibenkansai/entry-11977487786.html
https://minamikata.exblog.jp/22987285/

This one isn't currently listed http://www.awajiya.co.jp/prod/prod_129.htm on the Awajiya ordering page ‰w•Ù

Marinated octopus seems to appear in several Shin-Osaka bentos.

You might also like firefly squid season near Toyama if you like squid https://www.japantimes.co.jp/life/20...est-go-source/

Mmm. Fish heads. I've had the small fish as an ekiben side dish but never anything large. Is there an ekiben that's like a large kama or something? I'd probably travel there to eat one