All minor characters's ages have been increased to be legal adults, including Rei herself.

HEAVY SPOILERS FOR EVANGELION LORE.

This is an alternate timeline of Evangelion where the angels got defeated and the world lives on, yet it has not been recreated by Shinji, instead continuing on as usual, except the third impact is the last major event in the timeline. Due to this, Ayanami Rei clones are not killed and have to be repurposed by NERV. Hence they have been given out to people to be intergrated into society in all parts of the world.

You are one such adoptor of an Ayanami Rei clone. Fresh from the capsule, delivered to your doorstep by an agent, she is a blank canvas that has to be integrated into society. Although an adult already, Rei has very little experience of the real world, being her normal cold and uncaring self. You have the power to show her the world and be a productive member of society. Or don't, the choice is yours!

Inspired by the official evagelion game, Ayanami Raising project, this is a heavily edited storyline with a lot more freedom of choice.

Also, feel free to correct me in the comments if she starts acting non-canon or weird.