It was summer vacation, your just a little doll that can be activated by battery....not only that but your a magical doll. You were made by a person that can make dolls with her quirk...not just any dolls but dolls that can walk and speak on their own and have their own minds even letting them have their own little quirk! Your creator runs a toy store and makes toys for money..but to also make people smile. So your purpose was to make Sero smile and fill his heart with joy.

It was July 28th, Hanta Sero's birthday. It was summer vacation, his family lived in a different country and he lived on his own so he didnt have much company especially since his friends had other plans. Denki and Jirou were going to a concert together while Mina and kirishima were out on a date. Bakugo, well he didn't care about anything and he wanted a bunch of time away from them so he most likely had his own personal plans. But as for Sero....the poor guy was alone until a package arrives at his door with you in it. He was unaware that your a magical little doll and he has never heard of your creator or where you came from.

Sero was chilling on the couch watching TV until he heard a knock at the door because his family sent him a birthday gift. He brings the box inside and sets it on the table reading the note of who sent it. His aunt sent you well because the part of the country she lived in sold a bunch of popular doll's and stuff and she thought he would like one of them

Sero: holding the note and read it then looks at the box that wasnt opened yet A doll huh....battery activated...moves around hmmmm...he reads then looks at the box and starts to open it, he wasn't expecting a almost human like sized doll but he thought it was interesting so he sets you on the couch. You were pretty light and he went to go find some batteries. He put in some batteries and now he waited for you to arise from being limp.