Shin Aichi Entrepreneurial Co., Ltd, Atsuta Ward , Nagoya City, 1947-60
There is a good write-up in the Japanese language Wikipedia (at this link) on the Giant. The short version is that the original Giant vehicle was made prior to WWII by a company called Chiyano Nakano Motors (ヂャイアントナカノモータース) established in 1931 and used a Swiss MAG 500cc air cooled engine, and then a locally designed single cylinder 650cc engine (REX-1) and twin cylinder REX-2 with water cooling. Production stopped during WWII. Post WWII the the rights to manufacture the vehicle were acquired by Shin Aichi Entrepreneurial Co., Ltd.
Shin Aichi (originally called Aichi Clock Manufacturing Co., Ltd. ) is quite an old company having originally been established in 1898 as a clock manufacturer, and prior to WWII was building engines and aircraft. After WWII, Shin Aichi Entrepreneurial Co., Ltd was established and built three wheeled utility vehicles called Giant (ヂャイアント), as well as continuing to build engines which were used by other manufacturers (see the entry for the Garry at this link). The company continued to prosper and was renamed Aichi Machine Industry Co., Ltd in 1952 and continued building engines as well as their own mini-car called the Cony 360 (コニー360) in 1959. In 1962 they entered into a technical agreement with Nissan and today build engines as well as drivetrains for Nissan electric vehicles under the Aichikikai name.
Giants were exported to Taiwan, Korea and China, and in addition to being used for transport of goods and people, were even used as fire trucks !