Still somehow never driven a proper kei car. Closest I've got is a UK market Suzuki SC100, which fits to kei dimensions but has a 1-litre engine instead of the sub-550cc two-stroke triple of the JDM Cervo.
Lovely little thing to drive though. Didn't feel like an "economy car" at all - the interior was as well-appointed as something like a 240Z, with proper instruments, a full dashboard, and surprisingly little bare metal showing through.
Unfortunately only a few keis have ever made it to the UK officially and unchanged from the proper spec. The Cappuccino was one, the Daihatsu Copen another, and both the petrol and electric versions of the Mitsubishi i. Our Daihatsu Move was too big in both scale and engine. Original Smart City Coupes/Smart Fortwos nearly conformed to kei regs (they were short enough and had small enough - 600cc - engines) but were slightly too wide, so a kei-specific version was sold in Japan.
Aside from the Daihatsu Midget II, which will forever be a favourite thanks to Gran Turismo, one of my favourite keis is probably the Daihatsu Naked:
I'd love to import one at some stage, but the exchange rate makes that far too unfavourable at the moment.