Two teenagers dressed in Gothic-style clothes were subjected to a violent attack at the hands of three girls, police said.
Detectives are investigating whether the assault, during which one victim was kicked and punched 17 times, may have been a "hate crime" motivated by the pair's attire.
The attack happened outside a newsagent in Mersey Square, Stockport, at about 9.30pm on July 15.
A teenage boy was sat on a wall when he was approached by three teenage girls who verbally abused him without provocation, police said.
He was then punched 10 times and kicked on seven occasions in the space of a minute.
A teenage girl was also punched in the head during the incident, which came to an end when a woman on a bike intervened and the assailants walked off.
Greater Manchester Police said both victims were dressed in Gothic-style clothing and the force is investigating whether this was a "motivating factor".
Last year the force became the first to record offences committed against Goths, or other "sub-culture" groups, as hate crimes in the same way as with offences aimed at race, disability or sexual orientation.
A campaign for the change was led by Sylvia Lancaster, whose daughter Sophie, 20, was battered to death because of her Goth appearance by a gang of thugs in 2007.
Neither victim in the latest incident has come forward and police are urging them to contact police to record a crime. Officers are also keen to speak to the bike rider who stepped in.
The male victim was described as white, in his teens, with red hair, and was wearing a long dark jacket, dark trousers with chains and boots.
The girl who was assaulted was said to be also white, with auburn hair and also wearing Gothic-style clothing.
Pc Steve Watson said: " Until we have spoken to the two victims we cannot be certain if this attack was a hate crime motivated by the clothing the victims were wearing, but clearly we have to consider that as an aggravating factor.
"Greater Manchester Police takes all reports of hate crime extremely seriously and... we are now recording crimes where alternative sub-cultures are targeted for their identity and distinctive clothing.
"People who wish to express their alternative sub-culture identity freely should not have to tolerate hate crime and therefore I would strongly urge both victims to come forward so we can record their complaints and ensure those responsible are punished appropriately.
"It is totally abhorrent for anyone to be attacked because of a distinctive identity, and the level of violence the young boy was subjected to - 17 blows in just 60 seconds - is an appalling indictment of the behaviour of those responsible. He is lucky he was not seriously injured.
"So I would again urge the victims to please call us and we will offer you whatever support you need."