The group are a five piece dance troupe from The Wirral, made up of best friends Alice (17), Poppy (14), Julia (15), Annie (17) and Rebecca (16).
"No one's ever going to come between our friendship and that's why it's just us," the girls told cameras during their audition earlier this month.
Speaking to the panel before their performance, Julia revealed she has Scoliosis and will soon undergo surgery which will leave her unable to dance.
"This is my last chance and I've always wanted to do it," she said.
Just Us turned MerseyGirls went on to perform to Rachel Platten's Fight Song.
After the routine, a teary Alesha Dixon said: "I have so much admiration for you girls right now, I can't tell you. Seeing how you come together, when you're passionate about something I can't imagine not being able to ever do that again.
"I really couldn't and that's why we all live, for the things we love to do. It really touched me."
She then hit the golden buzzer to send the group straight into the live shows which started on Monday.
A number of other acts through to the semi-finals have also had changes to their names.
Dance group TNG have become TNG Characters, girl group Miss Treats have become Miss Treat Vibe and the Pensionnaires are now known as the Pensionalities.
The Britain's Got Talent 2017 live shows air from Monday, May 29 until Friday, June 2.
The semi-finals will air from 7:30PM on ITV with a group contestants performing each evening and two acts will make it through.
The ten finalists will then go head to head in the grand finale this SATURDAY night, June 3.