Qantas partner Japan Airlines will upgrade its domestic flights with new business and economy seats plus inflight Internet from the middle of this year as part of its ambitious JAL Sky Next refresh program.

Some 77 aircraft in JAL's short-range Boeing fleet are in line for the make-over, including nine of the twin-aisle Boeing 767-300ER jets which will also be fitted with an exclusive first class cabin.

The first member of the renewed JAL Sky Next fleet is expected to begin flights in May, although the airline has not yet revealed which routes will see the beefed-up Boeings.

JAL's new recliner business class seats will be covered in leather and configured with 38 inch pitch and an extra-wide armrest between seats.

Their economy siblings are also leather-clad and use a molded slimline design to reduce weight and increase effective legroom while retaining a 31 inch pitch, with JAL listing them as 5cm (2 inches) thinner than conventional economy seats.

The upgraded Boeing 767-300s with first class will begin flying in late 2014, JAL says.

As each Sky Next jet is overhauled it will also receive a refreshed cabin with LED lighting which JAL says will change "the cabin atmosphere  according to the flight hours, the season, and the natural rhythm of time to create a relaxing ambience and a feeling of Japan."

The WiFi service will be launched in July 2014 and will beam JAL's inflight entertainment content throughout the aircraft for free, with Internet based on Gogo's high-speed satellite system available for a fee.

JAL will offer Internet access in a half-hour block for ¥400 (A$4.50). Unlimited plans will range from ¥500 (A$5.60) for a smartphone on all domestic routes to ¥500, ¥700 and ¥1200 for tablets and laptops depending on the length of the flight.

Diamond, Premier and Sapphire members of JAL's Mileage Bank frequent flyer program will receive free WiFi coupons every year.

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