A 51-year-old from Belfast has appeared in court charged with rape and a string of other grooming offences.
The man, who cannot be named for legal reasons, allegedly raped a schoolgirl and blackmailed another into sending him naked images after posing online as a teenage boy.
He used a fake social media profile to "catfish" young girls for pleasure, the court heard.
The offences allegedly took place between 1 July 2019 and 28 March.
They include two counts of rape, threats to kill, attempting to meet a child following sexual grooming, causing a child to watch sexual activity and sexual communication with a child.
The man, who appeared at Belfast Magistrates' Court, is further accused of sexually touching a girl who was unable to refuse due to a mental disorder, harassment and blackmail as well as possessing and distributing indecent images of a child.
The defendant was arrested after Derbyshire Police raised concerns about the potential grooming of a number of girls aged between 13 and 14, the court heard.
A detective said the accused had disguised himself as a 13-year-old boy on Instagram and Snapchat to obtain indecent images.
One alleged victim believed she was in a relationship with him and planned a meeting in England, according to police.
The court heard some images received from one girl were then sent on to as many as seven other girls.
A defence solicitor said the accused was vulnerable and suggested he may not have understood what he said during police interviews.
However, the judge ruled that the defendant must be remanded in custody due to concerns about any further offences.
Refusing bail, he said: "These are very serious charges, dealing with some of the most vulnerable people we have in our community."