Rahman, of Ballards Lane, in Finchley, north London, is also charged with assisting Imran in terror planning. When asked about his nationality in court, Imran said he was Bangladeshi British.
"The secondary attack was to be carried out with a suicide vest, pepper spray and a knife", he told the court.
Rahman was carrying two inert explosive devices when he was arrested last week, the court heard.
Later it became known that the responsibility for what happened in Manchester, the attack claimed by the terrorist group "Islamic state". The statement made no reference to the alleged target. The recording would have given Imran greater credibility with the terrorist organization, the document said.
Rahman and Imran gave no indication as to their plea so a not guilty plea was entered on their behalf.More news: Knicks SG Tim Hardaway Jr. out at least two weeks
They are due to appear in Westminster Magistrates' Court on Wednesday.
Two men were arrested last week following a joint operation by MI5, the UK's counter-terrorism security service, and police. Nobody was injured during that attack. An official report released Tuesday on a suicide bombing that killed 22 people at the Manchester Arena in May found that opportunities to thwart the attack had been missed.
"On two separate occasions in the months prior to the attack, intelligence was received by MI5 whose significance was not fully appreciated at the time", the report said. It will look at whether the attacks could have been averted.
"The UK is facing an intense threat from terrorism, one which is multi-dimensional, evolving rapidly and operating at a scale and pace we have not seen before", London's Metropolitan Police said on Tuesday.
Officials said it was the 22nd foiled plot since March as hundreds of terrorist suspects remain under investigation.