You can seal the wood without stain.
Stain is not natural. Just use a varnish over raw wood. Will need to sand between coats and before you varnish.
Is one of the vinegar and steel wool projects the one that gave you this idea? I found quite a few project created by other Hometalk members using steel wool & vinegar. I'm hoping this will help. Wishing you the best.
Here's a post that might help - https://www.diynatural.com/homemade-wood-stain/
I too have seen the vinegar and steel wool. There are some with coffee, pennies..just all sorts. It does not cover as well as store bought stain but they definitely put some color in.