In September 1942, Warrant Officer Haruzo Ota and FCPO Sakai served as pilots on the seaplane tender Kunikawa Maru .

The Kunikawa Maru departed Truk on 8 September 1942 with an air group of six F1M Pete floatplanes. It was carrying materials and personnel to begin construction of an airfield at Buin in southern Bougainville. After leaving the Shortlands on 10 September it was also tasked with scouting locations in the Solomons suitable for use as forward seaplane bases.

On 11 September 1942, PBY 11-P-10 from VP-11 was flying a search patrol from Ndeni when it was shot down at 09:30 east of Malaita. IT had been shot down by a pair of Pete floatplanes from the Kunikawa Maru flown by Warrant Officer Haruzo Ota and FCPO Sakai. Both pilots were jointly credited with the flying boat as the unit’s first combat kill.
The eight-man PBY crew under Lieutenant Carlton H Clark was collected by the destroyer Murasame and then transferred to the cruiser Atago the following day. The crew were eventually transported to Japan where two of the crew died as POWs, with the remainder eventually liberated from the Shinjuku POW camp near Tokyo.

Sakai ended the war with 1 shared biplane victory.

Claims:

Kill no.	Date	Time	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1942
	11/09/42	09:30	1/2	PBY (a)	Shared destroyed	F1M		E Malaita	Kamikawa Maru

Biplane victories: 1 shared destroyed.
TOTAL: 1 shared destroyed.
(a) PBY 11-P-10 from VP-11 shot down with Lieutenant Carlton H Clark and crew becoming POWs.

Sources:
Solomons Air War Volume 1: Guadalcanal August - September 1942 - Michael John Claringbould and Peter Ingman, 2023 Avonmore Books, ISBN 978-0-6452469-3-3
Solomons Air War Volume 2: Guadalcanal & Santa Cruz October 1942 - Michael John Claringbould and Peter Ingman. 2023 Avonmore Books, ISBN 978-0-645-70045-9