hello there, I’m making my first character ever and I’m having trouble with his backstory because I still know very little about the d&d world. His name’s Joan, son of an earth genasi and a human. His grandmother is a genie and she’s stuck inside him. I can’t figure out how she got stuck. I figured Joan did something he shouldn’t and as punishment got stuck with his grandma genie, who had to take responsibility for him. Like I said, I don’t know how. Is there a spell that can do that? Can another more powerful creature do that, and would they? 

I really want her to be a constant voice in his head, mostly because it’s going to be funny, but also because Joan needs to learn how to not be jerk. You know, for character development. If you know any lore that could answer this situation, or have an idea on how it could go down, please answer. 

Edit: Thanks for replies, they are greatly appreciated❤️

This will mainly depend on the lore of the world you are playing in and something you should talk to your DM about.

I'd suggest a cursed item as they can't be removed easily.

Since Genassi are planetouched, some sort of Warlock could work. That way, your patron gives you power, but the added "curse" of your Granny. Celestial, or Fiend... but this curse/power thing seems like Fey.

Unless you already have a class picked out...

This is a technicality, but seems like the kinda thing you're asking about: 

Earth aspects djiini are actually called Dao. Dao are also lawful evil, insanely greedy, and slave takers. You can make your granny along those lines, or have her be an outlier and be good, but just be aware that would be very outside the norm. Maybe that's why she was imprisoned by the rest of her kind for deviating. Or maybe she was imprisoned for being greedier and more wicked than her kind and they saw her as too much of a threat to their own wealth. 

As for "can something imprison...etc" no, there's no specific spell for it, but there doesn't need to be. Magic isn't just what's laid down in the book. If it's part of your story, and the DM says it meshes with the world they made, then it works. 

Just some thoughts. 

*EDIT,

Just noticed you wanted the character to be the punished one, not the granny.  In that case, maybe the thing Joan did to earn their punishment is in some way related to the greed he may have inherited from his dao ancestors. 

Cursed item, ey, that sounds cool. I also don't have a DM to ask, but when I get in touch with one I shall ask. Thanks for replying.

I shall keep this in mind when I find someone to play with. Thanks for replying.

I already made him a fighter class, but warlocks sounds interesting, maybe I can read up on that and play around with it for my next character. Thank you for replying and giving me this info.

Yeah, I did read about the Dao, I don't know if granny's evil or good yet, however I know she's not a very good person. If she's chaotic good or evil, I don't know which direction to go in. She did fall in love a human ones, but she could have an alternative motive to try and manipulate Joan. 

All his life Joan has always wanted peace and quiet, however, maybe there's an underlying material desire that could poke it's head out when he optains it.

anyway, thank you for replying, I love figuring put twists and turns for characters. I really want to play as Joan to see where he goes.