[1] He was a member of the Tainan Kōkūtai's famous "clean up trio" with fellow aces Saburō Sakai and Toshio Ōta and would see action in the New Guinea campaign as well as in the aerial battles over Guadalcanal and over the Solomon Islands.

In June 1936, a poster caught his eye, an appeal for volunteers to join the Yokaren (flight reserve enlistee training program).

[4] After the outbreak of war with the Allies, Nishizawa's squadron (chutai) from the Chitose Air Group, then flying the obsolete Mitsubishi A5M, moved to Vunakanau airfield on the newly taken island of New Britain.

On 3 February 1942, Nishizawa, still flying an obsolete A5M, claimed his first aerial kill of the war, a PBY Catalina; historians have established, however, that the plane was only damaged and managed to return to base.

Sakai described his friend Nishizawa as about 173 cm (5 ft 8 in) tall, 63 kg (140 lb) in weight, pale and gaunt, suffering constantly from malaria and tropical skin diseases.

Of his performance in the air, Sakai, himself one of Japan's leading aerial aces, wrote, "Never have I seen a man with a fighter plane do what Nishizawa would do with his Zero.

Nishizawa, thinking about this mysterious skeleton dance, now suddenly had a crazy idea: "you know the mission tomorrow at Port Moresby?

On 17 May 1942, Lieutenant Commander Tadashi "Shosa" Nakajima led the Tainan Ku on a mission to Port Moresby, with Sakai and Nishizawa as his wingmen.

The letter, written in English, said:[5] To the Lae Commander: "We were much impressed with those three pilots who visited us today, and we all liked the loops they flew over our field.

Nishizawa, Sakai and Ōta stood at stiff attention and tried to suppress laughing out loud, while Lieutenant Sasai dressed them down over their "idiotic behavior" and prohibited them from staging any more aerobatic shows over enemy airfields.

On 8 August 1942, Saburō Sakai, Nishizawa's closest friend, was severely wounded in combat with U.S. Navy carrier-based bombers.

Struck in the head by a bullet, covered with blood and blind in one eye, he returned to base in his damaged Zero after a four-hour, 47-minute flight over 560 nmi (1,040 km; 640 mi).

In frustrated concern, Nishizawa physically removed the waiting driver and personally drove Sakai, as quickly but as gently as possible, to the surgeon.

In mid-November, the 251st was recalled to Toyohashi air base in Japan to replace its losses, with the ten surviving pilots all being made instructors, including Nishizawa.

Nishizawa is believed to have had around 40 full or partial aerial victories by this time (some sources claim 54).Nishizawa, while staying in Japan, visited Saburō Sakai, who was still recuperating in the Yokosuka hospital.

Nishizawa complained to Sakai of his new duty as an instructor: "Saburō, can you picture me running around in a rickety old biplane, teaching some fool youngster how to bank and turn, and how to keep his pants dry?"

Nishizawa also ascribed the loss of most of their comrade pilots to the ever increasing material advantage of the Allied forces, the improved U.S. aircraft and tactics.

In June 1943, Nishizawa's achievements were honored by a gift from the commander of the 11th Air Fleet, Vice Admiral Jin'ichi Kusaka.

On 25 October 1944, Nishizawa led the fighter escort consisting of four A6M5s, flown by Nishizawa, Misao Sugawa, Shingo Honda and Ryoji Baba for the first major kamikaze attack of the war, targeting Vice Admiral Clifton Sprague's "Taffy 3" task force, which was protecting the landings in the Battle of Leyte Gulf.

Instead, Nishizawa's A6M5 Zero was armed with a 250 kg (550 lb) bomb and flown by Naval Air Pilot 1st Class Tomisaku Katsumata.

Over Calapan on Mindoro Island, the Ki-49 transport was attacked by two F6F Hellcats of VF-14 squadron from the fleet carrier USS Wasp and was shot down in flames.