I think I found a webnovel about tulpas.

So I just wanted to mention this real quick, there's a webnovel about forty chapters long called "grace dances opon clouds."

Ive only read the first four or five chapters but it's pretty good, it's basically about this boy who has this dream world that's incredibly vivid and a tulpa like girl named grace appears in his dream world and they go on adventures together and she also teaches him to do certain things in the real world. You guys should check it out.