Breaking with the biplane tradition which had been the rule until that same moment, both companies submitted monoplane designs with Nakajima submitting a navalized version of their Army Type 91 fighter which was already in service with the Imperial Japanese Army.
Mitsubishi assigned the design of its contestant to a team led by Jiro Horikoshi (the same designer of the mighty A6M Zero) who eventually created the first low-wing cantilever monoplane to be designed in Japan, the Mitsubishi 1MF10.
The Mitsubishi 1MF10 (AKA Mitsubishi Experimental 7-Shi Carrier Fighter) was made entirely out of all-metal with a monocoque duraluminium fuselage, with duraluminium wing structure covered in fabric, with an open cockpit. It was powered by a single Mitsubishi A4 14-cylinder air-cooled radial engine which yielded 780hp (580Kw) of power which drove a two-bladed wooden propeller. It had a fixed undercarriage, both main and tailwheel.
The first prototype, with the internal company name of Mitsubishi Experimental 7-Shi Carrier Fighter, flew for the first time in March 1933 and the first prototype was destroyed shortly later, in July 1933, due to a broken tail during diving tests, although the pilot successfully jumped out of the cockpit by parachute. The second prototype, which had a slightly modified undercarriage, with the main wheels and undercarriage legs faired into streamlined spats, was also destroyed in a crash when it entered an uncontrolable dive spin in June 1934 when it was being piloted by Motoharu Okamura who bailed out in time to save his life but at the cost of four fingers, jeopardizing that way his career as fighter pilot.
Although the design was advanced for its time (it was comparable to the American Boeing P-26), it wasn't accepted by the Imperial Japanese Navy because it had poor handling and it didn't meet the requirements of the specification. However, it did form the basis for more advanced designs as Horikoshi used elements of it (like the box-spar) in the later successful design like the Mitsubishi A5M fighter which had similar layout.
Sources:
1. https://en.wikipedia.org/wiki/Mitsubishi_1MF10
2. https://en.wikipedia.org/wiki/Motoharu_Okamura
3. Salamander Books - The Complete Book of Fighters
