More pics

 

There is a chance that the floor was built to take all the load but most of the time they take the cheaper route and make that wall or a post a the corner load bearing. With out seeing the original plans it would be some considerable destruction to prove it one way or the other.
Here is a sample where they put beams around the stairs but still use that corner supported from below, and there is a header for the top of the stairs

But it can be framed in the floor like this one,

Just to investigate what you have would mean a fair amount would have to be opened and there would be a good chance of a disappointment.

 

Thank you that helps a lot! If we opened it up anyways and discovered the front was load bearing like the first picture could we still take out the rest of it and leave those posts? I could always make it into a reading corner or something else. It would still give him more space instead of a giant closet he would never use.

 

Maybe, more investigation for that.
Are there walls directly above that section which would add to the load?
Do you know the direction of the joists?
Usually but not guaranteed when the lower wall is load bearing there would be a single joist next to the stairs. And when the wall is not load bear the joist would be double.

You might learn a lot by taking down some of the ceiling at the corner, I have marked it in red.

 

Theres a chance the back wall provides intermediate support for the stairs.

 

Theres a chance the back wall provides intermediate support for the stairs.
View attachment 792697

I have never seen a footing for that.

 

I have put a header in this wall and a full sized door and just drywall the side of the stringer that is exposed.

 

We did some investigating…

 

That does not tell us much, unless you have bolts holding the wall to the floor, assuming this is a basement?

 

The corner posts could be supporting the header of the opening in the floor above. You already have a gap in the ceiling to patch, you should open it up more as neal suggested.