The OW Visit Asia pass, which you have to buy in conjunction with a OW ticket to/from Asia, allows you to buy as many segments as you want (2 minimum) in Asia for a set price per segment (details are on the OW site). It appears from the pricing etc. that these can only be in Y (no J or F).

You don't say how you are going to get to/from Asia? Most people around here are doing round the world tickets but that doesn't help you if you just want to go to Asia (the minimum RTW ticket you could do would be 3 continents, probably Europe -> Asia -> North America -> Europe.

I can't say if the Visit Asia pass is a 'good value'. You'd really have to decide what your routing is (perhaps, say, LHR-NRT-ICN-HKG-LHR) and then find out what that ticket would cost versus the cost of doing, say, LHR-NRT-LHR plus a Visit Asia pass to get you NRT-ICN-HKG-NRT.