Does that panel open to anything important? If not, my instinct is to put the storage against that wall, facing out to the room, rather than where it is now, in deeper gloom. If you're creative, you could probably even find stepped storage that will fit the angle, like stacked storage cubes or something similar.

Is that a white board or a door? What is on that little table? Router? https://www.homify.sg/ideabooks/831008/12-ingenious-ways-to-use-your-under-stair-space