The Japanese are working on their own stealth fighter, and they appear to be favoring a large weapons load over agility: (Paid subscription required)
With each published design iteration, Japan’s proposed indigenous fighter appears to be large, perhaps matching the size of the Lockheed Martin F-22 Raptor.
Actually, it is even bigger.
Drawing up a concept that emphasizes weapon load and endurance over maneuverability, designers at the Japanese defense ministry have come up with an aircraft that is longer than the F-22 and has a considerably greater wingspan. It is low in profile, however, to minimize radar reflections from the side.
Official drawings of the proposed aircraft and the model used for weapon-ejection testing show that 26DMU has few differences from the previous iteration, 25DMU. Bulges under the wing roots have been given a revised shape, maybe for aerodynamic reasons. On the model the tips of the main plane are straight, compared with a slightly pointed design on 25DMU. But the major features are unchanged. The design still has two belly bays each holding three big missiles, side bays with one short-range missile each, a wide and shallow fuselage, heavily canted tail surfaces and a large wing of high aspect ratio for efficient cruise and loitering.
The miniature missiles in the left belly bay of the model, which had an opened door for the tests, were Meteors with cropped fins, presumably of the design developed by MBDA for internal stowage in the Lockheed Martin F-35. The bay was only just large enough to hold three Meteors, mounted side by side and slightly staggered for tighter lateral packing. If Japan were willing to accept a rocket-propelled air-to-air weapon, the bay could also accommodate three missiles using the airframe of the Mitsubishi Electric AAM-4. Based on the Raytheon AIM-7 Sparrow, the AAM-4 has about the same length as the Meteor, 3.7 m (12 ft.).
Note that the AAM-4 and AIM-7 Sparrow are larger than the AIM-120 AMRAAM, having a body diameter of roughly 200mm, as opposed the 175mm.
The superior range of the AIM-120 comes from two things: Improvements in propellant, which could apply to the larger missiles as well, and improvements in flight profile during flight (more the 2nd than the first. By way of example, by updating avionics, the range of the SM-2 Standard was doubled by avionics changes which allowed it to take an indirect path to the target).
I guess is that the Japanese expect to deal with an opponent **cough** China **cough** at a significant distance from base without tanker support, so they need to carry more fuel and carry more missiles, because of potential threats from both long range interceptors (J-20 and Flanker derivatives) as well as very long range surface to air missiles (one would assume something north of 300 km, as the Russian SA-21 [S-400] exceeds 400 km).
By contrast, the F-22 was designed to fly from bases in the UK , the Netherlands, and Germany to engage Warsaw Pact aircraft at or behind the East-West German border, so there is a greater priority on agility. (Then again, the Raptor didn’t enter service until after the dissolution of the Warsaw Pact, which says something about how weapons procurement programs take on a life of their own.)