Nissan's former CEO appeared in a Tokyo court Wednesday in the trial of Greg Kelly, a former aide to Carlos Ghosn facing charges of financial misconduct.

Kelly is the only person currently on trial in Japan in connection with the Ghosn saga after the auto tycoon jumped bail in late 2019 and escaped to Lebanon, where he remains an international fugitive.

Kelly faces a single charge of conspiring to under-report tens of millions of dollars in pay that Ghosn was allegedly promised after his retirement.

Former Nissan CEO Hiroto Saikawa testified Wednesday that he had signed documents related to the alleged post-retirement payments on advice from Kelly, who argued Ghosn was being underpaid by global standards.

"The remuneration being paid then was low, so to make up for that we believed we needed a retirement package equivalent to or better than that at US companies," Saikawa said in court.

He said he understood the documents he signed to be drafted.

The trial against Kelly, which began in September, centers around one technical question: did Kelly and Nissan between 2010 and 2018 illegally conceal payments of around 9.2 billion yen ($87 million at today's rates) promised to Ghosn on retirement?

Nissan, which is also on trial over the alleged payments, says yes and has pleaded guilty, but Kelly has insisted on his innocence since he was detained in 2018.

Kelly has described Ghosn in court as an "extraordinary executive" who brought Nissan back from the brink of bankruptcy and was considered a "retention risk" because rules introduced in Japan from 2010 limited executive pay.

He has said various options for additional pay to Ghosn were considered, and he "took it for granted" that any compensation would be lawful.

But prosecutors and Nissan say they have evidence the future payments were pledged to Ghosn and therefore should have been disclosed in the firm's financial filings as required by Japanese law.

Kelly faces up to 10 years in prison if convicted in the trial, which is expected to run until summer.

Ghosn remains at large in Lebanon, but two men accused of helping him flee Japan are currently fighting extradition from the United States to Tokyo where they could face trial.