Okay, so a quick storytime on how this character was originally made-

So basically me and my best friend were talking about sans fangirls in Year 4/5 and I was like 'hey what if I made someone who looked like a fangirl but was his sister?' and thus the monstrosity on the left was born.

Anyways, the bow on the old design somehow contained her monster soul?? So basically you could hurt her as much as you wanted but unless you destroyed the bow she wouldn't die????

The bow for redeveloped Arial holds a lot more emotional and sentimental value. Basically, at some point of her living with the skelebros they were like, 'screw it, just give her a bow' and she loved it since it was like her first gift ever.

Anyways, the most interesting thing about the old Arial was that she ran away a lot-

New backstory: 

Arial is an experiment made to mimic the monsters' abilities. 

She is used as a 'spy' and gains more control of her power as she collects more data and sends it to her creator (who is purposefully ambiguous). 

She eventually cuts ties with her creator and somehow gets adopted by Sans and Papyrus despite being super shifty her whole time. 

She sometimes loses control of her power and accidentally uses people's powers against them (she didn't send all the data cuz she cut ties before she could).

And yes, she does have AU forms. I think her Storyshift one is my favourite (She's Little Miss Muffet in her Storyshift form, I'll upload it soon)