In addition to sharing expertise and manufacturing capabilities Musashi, which is 25% held by Honda Motor Corp, has invested an undisclosed amount in Aquarius.

The 10-kg engine can be used as an onboard power generator in a vehicle or as a stand-alone electricity generator. It is a single linear piston that blasts to and fro inside a valveless 800cc cylinder, generating power from electromagnetic coils with each stroke and with very low emissions.

"Musashi sees clear synergy with Aquarius Engines and their new system, which provides electrical mobility and charging while braking," Musashi CEO Hiroshi Otsuka said in a statement.

The two companies will initially co-develop the Aquarius electricity system to power 5G cellular base stations and supply electricity to remote areas and then progress to other markets, including the auto industry, he said.

(Reporting by Tova Cohen; Editing by Steven Scheer)