I already have a story for this, though the kid is a girl and the imaginary friend is trying to pursue a romantic relationship (despite the feelings being one-sided/the fact that's impossible.) <<that sounds so sweet!
Condensing a novel into a short, enticing book blurb that convinces readers to buy is no easy task. If you have no idea what to include in your blurb, this simple outline of the must-haves will help! Very helpful for synopsis.