As reported by One Mile at a Time, there is a ton of business class award space available on the new Japan Airlines flight from San Francisco to Tokyo Narita (they are adding a second daily flight on March 29, 2020). He reported 4 business class seats almost every day, including during cherry blossom season and the Olympics (some of which is already gone and will surely continue to get booked up, so hop on it now). Your best bet for booking these is with either Alaska Mileage Plan (60K one-way with a free stopover if you want though note you can’t mix with any other carrier other than Alaska — no continuing on from Japan on Cathay Pacific or something) or via American Airlines AAdvantage, which also charges 60K miles one-way in business class. Either can be booked online at their respective websites (if you want a stopover with Alaska, choose the multi-city search tool). This award space will surely get booked up quickly, so I’m keeping this short so you can book right now. Go.
H/T: One Mile at a Time