AirAsia's hub is Kuala Lumpur, Malaysia.
They currently have a 20% off offer and I've found a flight from Australia to Japan I like, which includes 7½ hours at
KUL in the middle of the night.
As far as I can tell if I book two separate flights, on their website, at the cheapest prices I can see, it's more expensive and will also incur the "hidden fees" of the site twice.
But is there a way to book the flight changing the layover to a stopover of a few days at KUL and still pay just the advertised discount fare (well plus the usual hidden fees of course).