23(Shadowhunters)

An Au where Magnus and Alec are girls and their first meeting and romance started differently then canon.

Magnus after the end of the fight with the Circle(the first one) was tired, she felt like everything was too much and wanted peace so she choose to not take the post as High Warlock and basically disappear from the map, only sending fire messages or calling her friends every few days but never revealing where she is.

Alec, loved her siblings but they kept ignoring her orders and acting like they knew what was the best so one day would arrive were Alec needed to just get away as she couldn't deal with that anymore especially with everyone assuming she loved Jace and when she fought him was because he was sleeping around with girls that weren't her. So, she requested to be moved to a small town where while there wasn't an actual Institute, they had a much smaller version of it, but at first her parents didn't agree but then she was able to convince them(maybe she said, it was for her to learn more on how to be a leader, or something like that).

It is in that small town that a 17 years old Alec meets a +400 years old Magnus, at first neither paid much attention to the other since unlike the other places, the small town was habited by downworlder, shadowhunters and mundanes that knew about each other and lived in harmony.

But there had been the appearance of an unknown creature that made them have to work together and they worked together perfectly and decided to try and get to know the other.

They grew closer and started falling in love but neither made a move to confess since they knew they would need to return to New York at some moment which happened a year later when Alec and Magnus were contacted by their friends/family about the appearance of Jocelyn and Clary and with that the news that Valentine wasn't dead.

While not together, they both valued the other a lot so they went to say their goodbye to each other only to find out they were both going to the same place and deal with the same problem...and that was what made them decided to say 'fuck it' and confess and at least share a kiss since they may die while trying to fight Valentine and his Circle.

Anything else is up to the writer, including how everyone else finds out about the two of them, if Alec still decides to become the HOTI or she and Magnus decide to return to the small town after defeating Valentine, etc.