What is Daiei and what does it sell?

I've seen two branches in Kumamoto and may even have been in one, but I can't remember.

Daiei is a department store/supermarket.

Some basic information
http://en.wikipedia.org/wiki/Daiei

Daiei is both a supermarket brand and department store brand in Japan.

Daiei is known for its low prices and its very plain looks (at least the ones I have visited).
A Japanese lady friend of a friend wouldn't be caught dead there, but if there is one near a hotel I stay in, I'll go to buy food, as it is cheaper than convenience stores.
Also a good place if you need cheap underwear, socks ..that type of things. Men clothes aren't great looking, ladies one aren't super stylish but in a pinch..they do...

If you are from the US, and you know what a SuperTarget is, Daiei is similar.

It's bunch of cheap Chinese-manufactured houseware and clothing, with a conventional grocery store inside.